<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:01a17520-7bd7-781a-90f6-8dfa26fae648,g:128238d5-45be-4873-837d-416f47a0c254-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://opalfuels.com/role/CoverPage" xlink:type="simple" xlink:href="wdq-20260930.xsd#CoverPage"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/CoverPage" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_01a17520-7df9-70dc-b2b9-33dbfd0767fd" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_DocumentInformationTable_01a17520-7df9-70dc-b2b9-33dbfd0767fd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_01a17520-7df9-7991-8fe2-60ad726105e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_01a17520-7df9-70dc-b2b9-33dbfd0767fd" xlink:to="loc_us-gaap_StatementClassOfStockAxis_01a17520-7df9-7991-8fe2-60ad726105e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7991-8fe2-60ad726105e9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a17520-7df9-7991-8fe2-60ad726105e9" xlink:to="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7991-8fe2-60ad726105e9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7edf-8c7d-dfab0e662256" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a17520-7df9-7991-8fe2-60ad726105e9" xlink:to="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7edf-8c7d-dfab0e662256" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_01a17520-7df9-7964-a598-80cb8923ba07" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7edf-8c7d-dfab0e662256" xlink:to="loc_us-gaap_CommonClassAMember_01a17520-7df9-7964-a598-80cb8923ba07" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_01a17520-7df9-7bd6-87d3-6120f2c04555" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7edf-8c7d-dfab0e662256" xlink:to="loc_us-gaap_CommonClassBMember_01a17520-7df9-7bd6-87d3-6120f2c04555" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_CommonClassDMember_01a17520-7df9-7d63-ab78-271cfc7f3b8e" xlink:href="wdq-20260930.xsd#wdq_CommonClassDMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7edf-8c7d-dfab0e662256" xlink:to="loc_wdq_CommonClassDMember_01a17520-7df9-7d63-ab78-271cfc7f3b8e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_01a17520-7df9-7bf0-bd6f-edd657640844" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_DocumentType_01a17520-7df9-7bf0-bd6f-edd657640844" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_01a17520-7df9-7c04-90f3-0ced91d90b09" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_DocumentQuarterlyReport_01a17520-7df9-7c04-90f3-0ced91d90b09" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_01a17520-7df9-7ba9-9502-8cb3c48d3da2" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_DocumentPeriodEndDate_01a17520-7df9-7ba9-9502-8cb3c48d3da2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_01a17520-7df9-7e1a-8888-9575bcd372da" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_DocumentTransitionReport_01a17520-7df9-7e1a-8888-9575bcd372da" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_01a17520-7df9-75ba-b0c4-a211968ebe88" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_EntityFileNumber_01a17520-7df9-75ba-b0c4-a211968ebe88" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_01a17520-7df9-7cdc-aa99-29d3e66c50c0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_EntityRegistrantName_01a17520-7df9-7cdc-aa99-29d3e66c50c0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_01a17520-7df9-7ed7-82ef-3934b37caecc" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_EntityIncorporationStateCountryCode_01a17520-7df9-7ed7-82ef-3934b37caecc" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_01a17520-7df9-7bd5-a812-b10f48ce132a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_EntityTaxIdentificationNumber_01a17520-7df9-7bd5-a812-b10f48ce132a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_01a17520-7df9-75b5-b383-b0567136cb8c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_EntityAddressAddressLine1_01a17520-7df9-75b5-b383-b0567136cb8c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_01a17520-7df9-73d9-85f7-9c0694b3ce94" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_EntityAddressAddressLine2_01a17520-7df9-73d9-85f7-9c0694b3ce94" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_01a17520-7df9-711d-92c7-ed21a8a55306" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_EntityAddressCityOrTown_01a17520-7df9-711d-92c7-ed21a8a55306" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_01a17520-7df9-755d-8020-2320f7a1a60b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_EntityAddressStateOrProvince_01a17520-7df9-755d-8020-2320f7a1a60b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_01a17520-7df9-735d-8c7a-94b5b4672ab4" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_EntityAddressPostalZipCode_01a17520-7df9-735d-8c7a-94b5b4672ab4" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_01a17520-7df9-7a82-82c9-542c46e22616" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_CityAreaCode_01a17520-7df9-7a82-82c9-542c46e22616" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_01a17520-7df9-746f-bd12-b2dd116a2c47" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_LocalPhoneNumber_01a17520-7df9-746f-bd12-b2dd116a2c47" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_01a17520-7df9-7b92-9a35-4edce416fcf6" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_Security12bTitle_01a17520-7df9-7b92-9a35-4edce416fcf6" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_01a17520-7df9-7616-a92d-b3dca3d9000b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_TradingSymbol_01a17520-7df9-7616-a92d-b3dca3d9000b" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_01a17520-7df9-7590-91fb-ef8c83c8dc10" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_SecurityExchangeName_01a17520-7df9-7590-91fb-ef8c83c8dc10" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_01a17520-7df9-7e0d-a855-ec208c960e6b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_EntityCurrentReportingStatus_01a17520-7df9-7e0d-a855-ec208c960e6b" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_01a17520-7df9-75be-9ff6-a817ac3d9310" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_EntityInteractiveDataCurrent_01a17520-7df9-75be-9ff6-a817ac3d9310" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_01a17520-7df9-7ead-be2b-774bad0881d8" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_EntityFilerCategory_01a17520-7df9-7ead-be2b-774bad0881d8" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_01a17520-7df9-7401-ba78-4fb36f68d4c6" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_EntitySmallBusiness_01a17520-7df9-7401-ba78-4fb36f68d4c6" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_01a17520-7df9-7034-8153-31f8978d6d6a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_EntityEmergingGrowthCompany_01a17520-7df9-7034-8153-31f8978d6d6a" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityExTransitionPeriod_01a17520-7df9-79a3-82fc-b9a939dbf83c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityExTransitionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_EntityExTransitionPeriod_01a17520-7df9-79a3-82fc-b9a939dbf83c" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_01a17520-7df9-7487-abe8-e31c37145166" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_EntityShellCompany_01a17520-7df9-7487-abe8-e31c37145166" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_01a17520-7df9-78f3-9dfb-9d2464ab537e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_01a17520-7df9-78f3-9dfb-9d2464ab537e" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_01a17520-7df9-7090-98ae-58175a0b7d11" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_EntityCentralIndexKey_01a17520-7df9-7090-98ae-58175a0b7d11" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_01a17520-7df9-70f6-ada5-0549a633c2e1" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_AmendmentFlag_01a17520-7df9-70f6-ada5-0549a633c2e1" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_01a17520-7df9-7554-b95c-5b55fdd32ae5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_DocumentFiscalYearFocus_01a17520-7df9-7554-b95c-5b55fdd32ae5" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_01a17520-7df9-761d-ac73-e3bb56861ece" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_DocumentFiscalPeriodFocus_01a17520-7df9-761d-ac73-e3bb56861ece" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_01a17520-7df9-725a-b74d-0d4da22a5065" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a17520-7df9-77c5-a4dc-7aa5ae7a0ad3" xlink:to="loc_dei_CurrentFiscalYearEndDate_01a17520-7df9-725a-b74d-0d4da22a5065" xlink:type="arc" order="30"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="simple" xlink:href="wdq-20260930.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETS"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a17520-7df9-70f1-a638-4bccbb6dc42e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_01a17520-7df9-77eb-9b94-abafdfa79a65" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-70f1-a638-4bccbb6dc42e" xlink:to="loc_us-gaap_StatementTable_01a17520-7df9-77eb-9b94-abafdfa79a65" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_01a17520-7df9-76e9-9008-f7b588d23253" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a17520-7df9-77eb-9b94-abafdfa79a65" xlink:to="loc_us-gaap_StatementClassOfStockAxis_01a17520-7df9-76e9-9008-f7b588d23253" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-76e9-9008-f7b588d23253_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a17520-7df9-76e9-9008-f7b588d23253" xlink:to="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-76e9-9008-f7b588d23253_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7ad6-8aa6-514475f84967" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a17520-7df9-76e9-9008-f7b588d23253" xlink:to="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7ad6-8aa6-514475f84967" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RedeemablePreferredNoncontrollingInterestMember_01a17520-7df9-7e7b-adb3-6d6684babb47" xlink:href="wdq-20260930.xsd#wdq_RedeemablePreferredNoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7ad6-8aa6-514475f84967" xlink:to="loc_wdq_RedeemablePreferredNoncontrollingInterestMember_01a17520-7df9-7e7b-adb3-6d6684babb47" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RedeemableNoncontrollingInterestMember_01a17520-7df9-72f6-8d9d-979c2d85d8ac" xlink:href="wdq-20260930.xsd#wdq_RedeemableNoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7ad6-8aa6-514475f84967" xlink:to="loc_wdq_RedeemableNoncontrollingInterestMember_01a17520-7df9-72f6-8d9d-979c2d85d8ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_01a17520-7df9-75a5-9bef-05b2d1027e50" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7ad6-8aa6-514475f84967" xlink:to="loc_us-gaap_CommonClassAMember_01a17520-7df9-75a5-9bef-05b2d1027e50" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_01a17520-7df9-7d21-9ce5-e081b5b36e51" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7ad6-8aa6-514475f84967" xlink:to="loc_us-gaap_CommonClassBMember_01a17520-7df9-7d21-9ce5-e081b5b36e51" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassCMember_01a17520-7df9-7b07-93bc-c612e38c94ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7ad6-8aa6-514475f84967" xlink:to="loc_us-gaap_CommonClassCMember_01a17520-7df9-7b07-93bc-c612e38c94ae" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_CommonClassDMember_01a17520-7df9-72fd-b3dd-9eeba4386e4d" xlink:href="wdq-20260930.xsd#wdq_CommonClassDMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7ad6-8aa6-514475f84967" xlink:to="loc_wdq_CommonClassDMember_01a17520-7df9-72fd-b3dd-9eeba4386e4d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_01a17520-7df9-7d3a-bcb1-242ac7985036" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-70f1-a638-4bccbb6dc42e" xlink:to="loc_us-gaap_AssetsAbstract_01a17520-7df9-7d3a-bcb1-242ac7985036" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_01a17520-7df9-751e-8c7a-2281ad9cfaed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a17520-7df9-7d3a-bcb1-242ac7985036" xlink:to="loc_us-gaap_AssetsCurrentAbstract_01a17520-7df9-751e-8c7a-2281ad9cfaed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_01a17520-7df9-7d9a-bb5b-3bd959e7022d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_01a17520-7df9-751e-8c7a-2281ad9cfaed" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_01a17520-7df9-7d9a-bb5b-3bd959e7022d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_01a17520-7df9-7e5b-9ccc-0898d15702e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_01a17520-7df9-751e-8c7a-2281ad9cfaed" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_01a17520-7df9-7e5b-9ccc-0898d15702e2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashCurrent_01a17520-7df9-7cd2-a458-3bd0de8e4d31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_01a17520-7df9-751e-8c7a-2281ad9cfaed" xlink:to="loc_us-gaap_RestrictedCashCurrent_01a17520-7df9-7cd2-a458-3bd0de8e4d31" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetCurrent_01a17520-7df9-75d9-bc29-66fc161623c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerAssetNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_01a17520-7df9-751e-8c7a-2281ad9cfaed" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetCurrent_01a17520-7df9-75d9-bc29-66fc161623c9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryPartsAndComponentsNetOfReserves_01a17520-7df9-73a0-a39c-f7bd489c24fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryPartsAndComponentsNetOfReserves"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_01a17520-7df9-751e-8c7a-2281ad9cfaed" xlink:to="loc_us-gaap_InventoryPartsAndComponentsNetOfReserves_01a17520-7df9-73a0-a39c-f7bd489c24fe" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrantsReceivableCurrent_01a1a9c9-8bbf-70f6-a1b9-f8a68f7287ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GrantsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_01a17520-7df9-751e-8c7a-2281ad9cfaed" xlink:to="loc_us-gaap_GrantsReceivableCurrent_01a1a9c9-8bbf-70f6-a1b9-f8a68f7287ca" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_01a17520-7df9-7993-98ca-872a554ec7c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_01a17520-7df9-751e-8c7a-2281ad9cfaed" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_01a17520-7df9-7993-98ca-872a554ec7c4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_01a17520-7df9-71f2-82d2-4e569bfe3e1c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_01a17520-7df9-751e-8c7a-2281ad9cfaed" xlink:to="loc_us-gaap_AssetsCurrent_01a17520-7df9-71f2-82d2-4e569bfe3e1c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_01a17520-7df9-7811-a022-5249ff71ed3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a17520-7df9-7d3a-bcb1-242ac7985036" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_01a17520-7df9-7811-a022-5249ff71ed3f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_01a17520-7df9-7d4d-81c0-53630d3a2a10" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a17520-7df9-7d3a-bcb1-242ac7985036" xlink:to="loc_us-gaap_EquityMethodInvestments_01a17520-7df9-7d4d-81c0-53630d3a2a10" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentInLeaseAfterAllowanceForCreditLoss_01a17520-7df9-7a12-9b13-69f48ed34c01" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetInvestmentInLeaseAfterAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a17520-7df9-7d3a-bcb1-242ac7985036" xlink:to="loc_us-gaap_NetInvestmentInLeaseAfterAllowanceForCreditLoss_01a17520-7df9-7a12-9b13-69f48ed34c01" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashNoncurrent_01a17520-7df9-7088-a3b8-7ca6a24a7d67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a17520-7df9-7d3a-bcb1-242ac7985036" xlink:to="loc_us-gaap_RestrictedCashNoncurrent_01a17520-7df9-7088-a3b8-7ca6a24a7d67" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_01a17520-7df9-7c65-bd8c-087ff712f5e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a17520-7df9-7d3a-bcb1-242ac7985036" xlink:to="loc_us-gaap_Goodwill_01a17520-7df9-7c65-bd8c-087ff712f5e4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_01a17520-7df9-7745-a7ac-c4eb2f444396" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a17520-7df9-7d3a-bcb1-242ac7985036" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_01a17520-7df9-7745-a7ac-c4eb2f444396" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_01a17520-7df9-7cb2-ad91-d12657ee07dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a17520-7df9-7d3a-bcb1-242ac7985036" xlink:to="loc_us-gaap_Assets_01a17520-7df9-7cb2-ad91-d12657ee07dc" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a17520-7df9-7b55-b85a-b85478f11901" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-70f1-a638-4bccbb6dc42e" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a17520-7df9-7b55-b85a-b85478f11901" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_01a17520-7df9-7f6b-8c7b-ac0da9120057" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a17520-7df9-7b55-b85a-b85478f11901" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_01a17520-7df9-7f6b-8c7b-ac0da9120057" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableOtherCurrent_01a17520-7df9-7608-befc-0b2f0e17cffe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableOtherCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a17520-7df9-7f6b-8c7b-ac0da9120057" xlink:to="loc_us-gaap_AccountsPayableOtherCurrent_01a17520-7df9-7608-befc-0b2f0e17cffe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_01a17520-7df9-75a2-820c-f546e130d02b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a17520-7df9-7f6b-8c7b-ac0da9120057" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_01a17520-7df9-75a2-820c-f546e130d02b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermConstructionLoanCurrent_01a17520-7df9-798c-9a26-878fbd5b95fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermConstructionLoanCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a17520-7df9-7f6b-8c7b-ac0da9120057" xlink:to="loc_us-gaap_LongTermConstructionLoanCurrent_01a17520-7df9-798c-9a26-878fbd5b95fb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAccruedLiabilitiesCurrent_01a17520-7df9-770a-98a4-3545b05419e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a17520-7df9-7f6b-8c7b-ac0da9120057" xlink:to="loc_us-gaap_OtherAccruedLiabilitiesCurrent_01a17520-7df9-770a-98a4-3545b05419e3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_01a17520-7df9-7b27-b578-3fa2b4396671" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a17520-7df9-7f6b-8c7b-ac0da9120057" xlink:to="loc_us-gaap_LiabilitiesCurrent_01a17520-7df9-7b27-b578-3fa2b4396671" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionLoanNoncurrent_01a17520-7df9-7f13-8b3b-4b6e372df640" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConstructionLoanNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a17520-7df9-7b55-b85a-b85478f11901" xlink:to="loc_us-gaap_ConstructionLoanNoncurrent_01a17520-7df9-7f13-8b3b-4b6e372df640" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_01a17520-7df9-7850-90df-938848b91d2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a17520-7df9-7b55-b85a-b85478f11901" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_01a17520-7df9-7850-90df-938848b91d2e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_01a17520-7df9-7199-b2bf-ebf520e39a33" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a17520-7df9-7b55-b85a-b85478f11901" xlink:to="loc_us-gaap_Liabilities_01a17520-7df9-7199-b2bf-ebf520e39a33" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_01a17520-7df9-77a9-aadd-cb92ff8d6ddf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a17520-7df9-7b55-b85a-b85478f11901" xlink:to="loc_us-gaap_CommitmentsAndContingencies_01a17520-7df9-77a9-aadd-cb92ff8d6ddf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_01a17520-7df9-7d2c-bf09-91c771e6bc0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a17520-7df9-7b55-b85a-b85478f11901" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_01a17520-7df9-7d2c-bf09-91c771e6bc0b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MembersEquityAbstract_01a17520-7df9-7f9d-bbdf-48f248bdaca8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MembersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a17520-7df9-7b55-b85a-b85478f11901" xlink:to="loc_us-gaap_MembersEquityAbstract_01a17520-7df9-7f9d-bbdf-48f248bdaca8" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_01a17520-7df9-71d1-88e9-94e465722950" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MembersEquityAbstract_01a17520-7df9-7f9d-bbdf-48f248bdaca8" xlink:to="loc_us-gaap_CommonStockValue_01a17520-7df9-71d1-88e9-94e465722950" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_01a17520-7df9-7709-a541-0ac13fabd29a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MembersEquityAbstract_01a17520-7df9-7f9d-bbdf-48f248bdaca8" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_01a17520-7df9-7709-a541-0ac13fabd29a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_01a17520-7df9-791e-a53e-fceec51c3741" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MembersEquityAbstract_01a17520-7df9-7f9d-bbdf-48f248bdaca8" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_01a17520-7df9-791e-a53e-fceec51c3741" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonValue_01a17520-7df9-7a9c-aaa5-6012550d5c06" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MembersEquityAbstract_01a17520-7df9-7f9d-bbdf-48f248bdaca8" xlink:to="loc_us-gaap_TreasuryStockCommonValue_01a17520-7df9-7a9c-aaa5-6012550d5c06" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a17520-7df9-79b7-9231-155ea9f125dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MembersEquityAbstract_01a17520-7df9-7f9d-bbdf-48f248bdaca8" xlink:to="loc_us-gaap_StockholdersEquity_01a17520-7df9-79b7-9231-155ea9f125dd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterest_01a17520-7df9-7eff-bbc2-113418dcdd15" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MembersEquityAbstract_01a17520-7df9-7f9d-bbdf-48f248bdaca8" xlink:to="loc_us-gaap_MinorityInterest_01a17520-7df9-7eff-bbc2-113418dcdd15" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_01a17520-7df9-7c4a-b456-33996e0c4ef3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MembersEquityAbstract_01a17520-7df9-7f9d-bbdf-48f248bdaca8" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_01a17520-7df9-7c4a-b456-33996e0c4ef3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_01a17520-7df9-761e-a1a3-585e130e1803" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a17520-7df9-7b55-b85a-b85478f11901" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_01a17520-7df9-761e-a1a3-585e130e1803" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="simple" xlink:href="wdq-20260930.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_01a17520-7df9-7361-8050-0dce76423e8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_StatementTable_01a17520-7df9-7361-8050-0dce76423e8f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_01a17520-7df9-7fa0-947f-08bc69a8243f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a17520-7df9-7361-8050-0dce76423e8f" xlink:to="loc_us-gaap_StatementClassOfStockAxis_01a17520-7df9-7fa0-947f-08bc69a8243f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7fa0-947f-08bc69a8243f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a17520-7df9-7fa0-947f-08bc69a8243f" xlink:to="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7fa0-947f-08bc69a8243f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7c27-981d-f4a5277f0ecb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a17520-7df9-7fa0-947f-08bc69a8243f" xlink:to="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7c27-981d-f4a5277f0ecb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_01a17520-7df9-7abe-b172-f9f0f28c354a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7c27-981d-f4a5277f0ecb" xlink:to="loc_us-gaap_CommonClassAMember_01a17520-7df9-7abe-b172-f9f0f28c354a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_01a17520-7df9-7d3c-bcce-63a3eca4d539" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7c27-981d-f4a5277f0ecb" xlink:to="loc_us-gaap_CommonClassBMember_01a17520-7df9-7d3c-bcce-63a3eca4d539" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassCMember_01a17520-7df9-7b26-bda8-48fab8796f39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7c27-981d-f4a5277f0ecb" xlink:to="loc_us-gaap_CommonClassCMember_01a17520-7df9-7b26-bda8-48fab8796f39" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_CommonClassDMember_01a17520-7df9-7651-b3fe-d23a8d3dc7f6" xlink:href="wdq-20260930.xsd#wdq_CommonClassDMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7df9-7c27-981d-f4a5277f0ecb" xlink:to="loc_wdq_CommonClassDMember_01a17520-7df9-7651-b3fe-d23a8d3dc7f6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a17520-7df9-7f11-a3ef-e64a452388a1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a17520-7df9-7361-8050-0dce76423e8f" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a17520-7df9-7f11-a3ef-e64a452388a1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a17520-7df9-7f11-a3ef-e64a452388a1_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_01a17520-7df9-7f11-a3ef-e64a452388a1" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a17520-7df9-7f11-a3ef-e64a452388a1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a17520-7df9-792c-9790-17304a505e36" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_01a17520-7df9-7f11-a3ef-e64a452388a1" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a17520-7df9-792c-9790-17304a505e36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_01a17520-7df9-7e9c-8a7d-d39bbeea1307" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_01a17520-7df9-792c-9790-17304a505e36" xlink:to="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_01a17520-7df9-7e9c-8a7d-d39bbeea1307" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7df9-7d07-865b-2a0181b1e7a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a17520-7df9-7361-8050-0dce76423e8f" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7df9-7d07-865b-2a0181b1e7a2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a17520-7df9-7d07-865b-2a0181b1e7a2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7df9-7d07-865b-2a0181b1e7a2" xlink:to="loc_us-gaap_RelatedPartyDomain_01a17520-7df9-7d07-865b-2a0181b1e7a2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a17520-7df9-7511-ac7a-4928c56ddf67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7df9-7d07-865b-2a0181b1e7a2" xlink:to="loc_us-gaap_RelatedPartyDomain_01a17520-7df9-7511-ac7a-4928c56ddf67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a17520-7df9-7f84-a4f9-8ce8accdb5e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a17520-7df9-7511-ac7a-4928c56ddf67" xlink:to="loc_us-gaap_RelatedPartyMember_01a17520-7df9-7f84-a4f9-8ce8accdb5e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrelatedPartyMember_01a17520-7df9-75f2-b98e-29395be232c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonrelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a17520-7df9-7511-ac7a-4928c56ddf67" xlink:to="loc_us-gaap_NonrelatedPartyMember_01a17520-7df9-75f2-b98e-29395be232c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_01a17520-7df9-7ef4-b3a6-62a05e306bd2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_01a17520-7df9-7ef4-b3a6-62a05e306bd2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_01a17520-7df9-735b-b0ee-94f7b43dde11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_01a17520-7df9-735b-b0ee-94f7b43dde11" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_01a17520-7df9-70ba-bdbd-c5bd77ea1715" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_CommonStockSharesIssued_01a17520-7df9-70ba-bdbd-c5bd77ea1715" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_01a17520-7df9-703e-a6b5-8f5d6448ac8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_01a17520-7df9-703e-a6b5-8f5d6448ac8f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_01a17520-7df9-7177-b01d-9f8039a5185d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_TreasuryStockCommonShares_01a17520-7df9-7177-b01d-9f8039a5185d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_01a17520-7df9-75ac-b7a5-1b6ddf3ddac6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_01a17520-7df9-75ac-b7a5-1b6ddf3ddac6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_01a17520-7df9-7978-a961-c8c8f7f00cf9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_01a17520-7df9-7978-a961-c8c8f7f00cf9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrantsReceivableCurrent_01a1bfa3-e865-7cec-afb7-761b4e36a296" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GrantsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_GrantsReceivableCurrent_01a1bfa3-e865-7cec-afb7-761b4e36a296" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashCurrent_01a17520-7df9-7083-86d2-e7c0a98f1f83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_RestrictedCashCurrent_01a17520-7df9-7083-86d2-e7c0a98f1f83" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_01a17520-7df9-752b-ab38-c7f8ca7ecd35" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_01a17520-7df9-752b-ab38-c7f8ca7ecd35" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_01a17520-7df9-7147-8233-b58738bc8c15" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_01a17520-7df9-7147-8233-b58738bc8c15" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashNoncurrent_01a17520-7df9-7a79-9120-ea7199d21f0f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_RestrictedCashNoncurrent_01a17520-7df9-7a79-9120-ea7199d21f0f" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_01a17520-7df9-7262-bb23-7d71bfb7f81d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_Assets_01a17520-7df9-7262-bb23-7d71bfb7f81d" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableOtherCurrent_01a17520-7df9-701f-b091-daa2f6f7ef18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableOtherCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_AccountsPayableOtherCurrent_01a17520-7df9-701f-b091-daa2f6f7ef18" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermConstructionLoanCurrent_01a17520-7df9-7f42-9f3a-e4a52c9ea764" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermConstructionLoanCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_LongTermConstructionLoanCurrent_01a17520-7df9-7f42-9f3a-e4a52c9ea764" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAccruedLiabilitiesCurrent_01a17520-7df9-768b-97b0-3b0ac6a63e30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_OtherAccruedLiabilitiesCurrent_01a17520-7df9-768b-97b0-3b0ac6a63e30" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionLoanNoncurrent_01a17520-7df9-7e13-9d41-e42df3a59b84" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConstructionLoanNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_ConstructionLoanNoncurrent_01a17520-7df9-7e13-9d41-e42df3a59b84" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_01a17520-7df9-7fdc-9284-3fce480d5ae0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_01a17520-7df9-7fdc-9284-3fce480d5ae0" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_01a17520-7df9-7560-89ad-8df276a72640" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-7a92-91e2-7b7abfedf723" xlink:to="loc_us-gaap_Liabilities_01a17520-7df9-7560-89ad-8df276a72640" xlink:type="arc" order="18"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="simple" xlink:href="wdq-20260930.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a17520-7df9-72c7-8a83-015e1876963e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_01a17520-7df9-77f1-8117-e6da1512f018" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-72c7-8a83-015e1876963e" xlink:to="loc_us-gaap_StatementTable_01a17520-7df9-77f1-8117-e6da1512f018" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7df9-7c43-9e1a-6777669fa253" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a17520-7df9-77f1-8117-e6da1512f018" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7df9-7c43-9e1a-6777669fa253" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a17520-7df9-7c43-9e1a-6777669fa253_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7df9-7c43-9e1a-6777669fa253" xlink:to="loc_us-gaap_SegmentDomain_01a17520-7df9-7c43-9e1a-6777669fa253_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a17520-7df9-758c-9690-45d2d56dc3de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7df9-7c43-9e1a-6777669fa253" xlink:to="loc_us-gaap_SegmentDomain_01a17520-7df9-758c-9690-45d2d56dc3de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RenewableNaturalGasFuelSupplySegmentMember_01a17520-7df9-7595-85d9-5bdf0cf20aa1" xlink:href="wdq-20260930.xsd#wdq_RenewableNaturalGasFuelSupplySegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a17520-7df9-758c-9690-45d2d56dc3de" xlink:to="loc_wdq_RenewableNaturalGasFuelSupplySegmentMember_01a17520-7df9-7595-85d9-5bdf0cf20aa1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_FuelStationServicesSegmentMember_01a17520-7df9-7786-aa77-c141f08d5209" xlink:href="wdq-20260930.xsd#wdq_FuelStationServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a17520-7df9-758c-9690-45d2d56dc3de" xlink:to="loc_wdq_FuelStationServicesSegmentMember_01a17520-7df9-7786-aa77-c141f08d5209" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RenewablePowerSegmentMember_01a17520-7df9-73e8-bd33-05d5185f3486" xlink:href="wdq-20260930.xsd#wdq_RenewablePowerSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a17520-7df9-758c-9690-45d2d56dc3de" xlink:to="loc_wdq_RenewablePowerSegmentMember_01a17520-7df9-73e8-bd33-05d5185f3486" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_01a17520-7df9-77e6-ba17-0355690c7157" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-72c7-8a83-015e1876963e" xlink:to="loc_us-gaap_RevenuesAbstract_01a17520-7df9-77e6-ba17-0355690c7157" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_01a17520-7df9-7f86-9965-7c44a69e0294" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_01a17520-7df9-77e6-ba17-0355690c7157" xlink:to="loc_us-gaap_Revenues_01a17520-7df9-7f86-9965-7c44a69e0294" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpensesAbstract_01a17520-7df9-7b95-9023-10e425af5a32" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-72c7-8a83-015e1876963e" xlink:to="loc_us-gaap_CostsAndExpensesAbstract_01a17520-7df9-7b95-9023-10e425af5a32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_01a17520-7df9-7146-9c64-fc63728a8a91" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_01a17520-7df9-7b95-9023-10e425af5a32" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_01a17520-7df9-7146-9c64-fc63728a8a91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_01a17520-7df9-7c65-a7d5-7c823385b5c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_01a17520-7df9-7b95-9023-10e425af5a32" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_01a17520-7df9-7c65-a7d5-7c823385b5c5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_01a17520-7df9-7bca-9d8e-041ea7e2fdae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_01a17520-7df9-7b95-9023-10e425af5a32" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_01a17520-7df9-7bca-9d8e-041ea7e2fdae" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAmortizationAndAccretionNet_01a17520-7df9-74bc-8347-c1df192421fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationAmortizationAndAccretionNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_01a17520-7df9-7b95-9023-10e425af5a32" xlink:to="loc_us-gaap_DepreciationAmortizationAndAccretionNet_01a17520-7df9-74bc-8347-c1df192421fc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TangibleAssetImpairmentCharges_01a17520-7df9-7310-ae52-efb2cff7a97d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TangibleAssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_01a17520-7df9-7b95-9023-10e425af5a32" xlink:to="loc_us-gaap_TangibleAssetImpairmentCharges_01a17520-7df9-7310-ae52-efb2cff7a97d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_01a17520-7df9-73e5-8d77-158d0be380a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_01a17520-7df9-7b95-9023-10e425af5a32" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_01a17520-7df9-73e5-8d77-158d0be380a6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_01a17520-7df9-7dfb-a374-72c1d1499c9c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_01a17520-7df9-7b95-9023-10e425af5a32" xlink:to="loc_us-gaap_CostsAndExpenses_01a17520-7df9-7dfb-a374-72c1d1499c9c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_01a17520-7df9-7f4c-ba4e-7459d393512c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-72c7-8a83-015e1876963e" xlink:to="loc_us-gaap_OperatingIncomeLoss_01a17520-7df9-7f4c-ba4e-7459d393512c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_01a17520-7df9-70c8-b0fa-5db1d7eb6207" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-72c7-8a83-015e1876963e" xlink:to="loc_us-gaap_InterestExpenseNonoperating_01a17520-7df9-70c8-b0fa-5db1d7eb6207" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeNonoperating_01a17520-7df9-7b84-933a-a6c46d4566cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-72c7-8a83-015e1876963e" xlink:to="loc_us-gaap_InvestmentIncomeNonoperating_01a17520-7df9-7b84-933a-a6c46d4566cc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_01a17520-7df9-776e-a36e-765567155726" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-72c7-8a83-015e1876963e" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_01a17520-7df9-776e-a36e-765567155726" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_01a17520-7df9-751d-ab7a-95b20e8e3e4c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-72c7-8a83-015e1876963e" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_01a17520-7df9-751d-ab7a-95b20e8e3e4c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a17520-7df9-7f32-862b-74956ac32dd9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-72c7-8a83-015e1876963e" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a17520-7df9-7f32-862b-74956ac32dd9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_01a17520-7df9-7e60-a44d-4030177b1c18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-72c7-8a83-015e1876963e" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_01a17520-7df9-7e60-a44d-4030177b1c18" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_01a17520-7df9-7fb4-b75f-40add202a764" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-72c7-8a83-015e1876963e" xlink:to="loc_us-gaap_ProfitLoss_01a17520-7df9-7fb4-b75f-40add202a764" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_01a17520-7df9-7438-b030-6dead03f247b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-72c7-8a83-015e1876963e" xlink:to="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_01a17520-7df9-7438-b030-6dead03f247b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNonredeemableNoncontrollingInterest_01a17520-7df9-7b77-b1ab-a8f2f1edb0dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAttributableToNonredeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-72c7-8a83-015e1876963e" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNonredeemableNoncontrollingInterest_01a17520-7df9-7b77-b1ab-a8f2f1edb0dc" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment_01a17520-7df9-7ec0-becf-88b3969d5fa5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-72c7-8a83-015e1876963e" xlink:to="loc_us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment_01a17520-7df9-7ec0-becf-88b3969d5fa5" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_01a17520-7df9-77a2-b3a3-13b0e27a2124" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-72c7-8a83-015e1876963e" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_01a17520-7df9-77a2-b3a3-13b0e27a2124" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_01a17520-7df9-79e7-9152-fc8c7bdb2df8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-72c7-8a83-015e1876963e" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_01a17520-7df9-79e7-9152-fc8c7bdb2df8" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_01a17520-7df9-767c-9850-eb5c605818ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_01a17520-7df9-79e7-9152-fc8c7bdb2df8" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_01a17520-7df9-767c-9850-eb5c605818ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_01a17520-7df9-7485-aeb6-d78f2424424d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_01a17520-7df9-79e7-9152-fc8c7bdb2df8" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_01a17520-7df9-7485-aeb6-d78f2424424d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareAbstract_01a17520-7df9-71fb-908e-d2c5a7cd917b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7df9-72c7-8a83-015e1876963e" xlink:to="loc_us-gaap_EarningsPerShareAbstract_01a17520-7df9-71fb-908e-d2c5a7cd917b" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_01a17520-7df9-7143-999a-0c2762b69972" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_01a17520-7df9-71fb-908e-d2c5a7cd917b" xlink:to="loc_us-gaap_EarningsPerShareBasic_01a17520-7df9-7143-999a-0c2762b69972" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_01a17520-7df9-7336-9394-1790efbe9162" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_01a17520-7df9-71fb-908e-d2c5a7cd917b" xlink:to="loc_us-gaap_EarningsPerShareDiluted_01a17520-7df9-7336-9394-1790efbe9162" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONSParenthetical" xlink:type="simple" xlink:href="wdq-20260930.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONSParenthetical"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONSParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a17520-7eab-7ac5-9882-ac845e513781" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_01a17520-7eab-7ecf-b0b0-5d621292ac30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7eab-7ac5-9882-ac845e513781" xlink:to="loc_us-gaap_StatementTable_01a17520-7eab-7ecf-b0b0-5d621292ac30" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7eab-7c08-b9b5-2562755a6cf3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a17520-7eab-7ecf-b0b0-5d621292ac30" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7eab-7c08-b9b5-2562755a6cf3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a17520-7eab-7c08-b9b5-2562755a6cf3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7eab-7c08-b9b5-2562755a6cf3" xlink:to="loc_us-gaap_SegmentDomain_01a17520-7eab-7c08-b9b5-2562755a6cf3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a17520-7eab-7cf3-8bae-3eff22020597" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7eab-7c08-b9b5-2562755a6cf3" xlink:to="loc_us-gaap_SegmentDomain_01a17520-7eab-7cf3-8bae-3eff22020597" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RenewableNaturalGasFuelSupplySegmentMember_01a17520-7eab-7b66-804b-946782aa6e31" xlink:href="wdq-20260930.xsd#wdq_RenewableNaturalGasFuelSupplySegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a17520-7eab-7cf3-8bae-3eff22020597" xlink:to="loc_wdq_RenewableNaturalGasFuelSupplySegmentMember_01a17520-7eab-7b66-804b-946782aa6e31" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_FuelStationServicesSegmentMember_01a17520-7eab-7423-a6c7-9f1d20d392ed" xlink:href="wdq-20260930.xsd#wdq_FuelStationServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a17520-7eab-7cf3-8bae-3eff22020597" xlink:to="loc_wdq_FuelStationServicesSegmentMember_01a17520-7eab-7423-a6c7-9f1d20d392ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RenewablePowerSegmentMember_01a17520-7eab-723b-a620-bdfa7858ac2f" xlink:href="wdq-20260930.xsd#wdq_RenewablePowerSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a17520-7eab-7cf3-8bae-3eff22020597" xlink:to="loc_wdq_RenewablePowerSegmentMember_01a17520-7eab-723b-a620-bdfa7858ac2f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7eab-7a89-b3ab-0f59e07e52ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a17520-7eab-7ecf-b0b0-5d621292ac30" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7eab-7a89-b3ab-0f59e07e52ee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a17520-7eab-7a89-b3ab-0f59e07e52ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7eab-7a89-b3ab-0f59e07e52ee" xlink:to="loc_us-gaap_RelatedPartyDomain_01a17520-7eab-7a89-b3ab-0f59e07e52ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a17520-7eab-7835-a18e-b0ab5d79e736" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7eab-7a89-b3ab-0f59e07e52ee" xlink:to="loc_us-gaap_RelatedPartyDomain_01a17520-7eab-7835-a18e-b0ab5d79e736" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a17520-7eab-72a6-8765-309e0ac48a6f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a17520-7eab-7835-a18e-b0ab5d79e736" xlink:to="loc_us-gaap_RelatedPartyMember_01a17520-7eab-72a6-8765-309e0ac48a6f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_01a17520-7eab-73e0-8552-915c1416902e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7eab-7ac5-9882-ac845e513781" xlink:to="loc_us-gaap_Revenues_01a17520-7eab-73e0-8552-915c1416902e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINREDEEMABLENONCONTROLLINGINTERESTREDEEMABLEPREFERREDNONCONTROLLINGINTERESTANDSTOCKHOLDERSEQUITYDEFICIT" xlink:type="simple" xlink:href="wdq-20260930.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINREDEEMABLENONCONTROLLINGINTERESTREDEEMABLEPREFERREDNONCONTROLLINGINTERESTANDSTOCKHOLDERSEQUITYDEFICIT"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINREDEEMABLENONCONTROLLINGINTERESTREDEEMABLEPREFERREDNONCONTROLLINGINTERESTANDSTOCKHOLDERSEQUITYDEFICIT" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a17520-7eab-7fd8-9a58-c89f7b5fa84b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_01a17520-7eab-7b22-b1ff-4467ba441c14" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7eab-7fd8-9a58-c89f7b5fa84b" xlink:to="loc_us-gaap_StatementTable_01a17520-7eab-7b22-b1ff-4467ba441c14" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_01a17520-7eab-78f4-8e76-ad19f226b001" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a17520-7eab-7b22-b1ff-4467ba441c14" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_01a17520-7eab-78f4-8e76-ad19f226b001" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a17520-7eab-78f4-8e76-ad19f226b001_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a17520-7eab-78f4-8e76-ad19f226b001" xlink:to="loc_us-gaap_EquityComponentDomain_01a17520-7eab-78f4-8e76-ad19f226b001_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a17520-7eab-7601-bbf3-4abb6fb22112" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a17520-7eab-78f4-8e76-ad19f226b001" xlink:to="loc_us-gaap_EquityComponentDomain_01a17520-7eab-7601-bbf3-4abb6fb22112" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_01a17520-7eab-725e-95da-e0ce2fa8de15" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a17520-7eab-7601-bbf3-4abb6fb22112" xlink:to="loc_us-gaap_CommonStockMember_01a17520-7eab-725e-95da-e0ce2fa8de15" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_01a17520-7eab-7a1a-852c-3c851339bf2f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a17520-7eab-7601-bbf3-4abb6fb22112" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_01a17520-7eab-7a1a-852c-3c851339bf2f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_01a17520-7eab-7c36-876e-1c2856504636" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a17520-7eab-7601-bbf3-4abb6fb22112" xlink:to="loc_us-gaap_RetainedEarningsMember_01a17520-7eab-7c36-876e-1c2856504636" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_01a17520-7eab-77ad-9b76-15b9248ddf65" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a17520-7eab-7601-bbf3-4abb6fb22112" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_01a17520-7eab-77ad-9b76-15b9248ddf65" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_01a17520-7eab-74ca-be26-9bd09155d368" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a17520-7eab-7601-bbf3-4abb6fb22112" xlink:to="loc_us-gaap_NoncontrollingInterestMember_01a17520-7eab-74ca-be26-9bd09155d368" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_01a17520-7eab-742e-90ba-a6f3a41e3ef2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a17520-7eab-7601-bbf3-4abb6fb22112" xlink:to="loc_us-gaap_TreasuryStockCommonMember_01a17520-7eab-742e-90ba-a6f3a41e3ef2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_01a17520-7eab-7e07-a370-b16e5a7cc688" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a17520-7eab-7b22-b1ff-4467ba441c14" xlink:to="loc_us-gaap_StatementClassOfStockAxis_01a17520-7eab-7e07-a370-b16e5a7cc688" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a17520-7eab-7e07-a370-b16e5a7cc688_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a17520-7eab-7e07-a370-b16e5a7cc688" xlink:to="loc_us-gaap_ClassOfStockDomain_01a17520-7eab-7e07-a370-b16e5a7cc688_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a17520-7eab-7c0e-beb2-2b8d4677a20c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a17520-7eab-7e07-a370-b16e5a7cc688" xlink:to="loc_us-gaap_ClassOfStockDomain_01a17520-7eab-7c0e-beb2-2b8d4677a20c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_01a17520-7eab-7609-bde7-7943abf744e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7eab-7c0e-beb2-2b8d4677a20c" xlink:to="loc_us-gaap_CommonClassAMember_01a17520-7eab-7609-bde7-7943abf744e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_01a17520-7eab-75e1-ac97-130165b8bf93" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7eab-7c0e-beb2-2b8d4677a20c" xlink:to="loc_us-gaap_CommonClassBMember_01a17520-7eab-75e1-ac97-130165b8bf93" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_CommonClassDMember_01a17520-7eab-7c8a-bf29-7928810a53e1" xlink:href="wdq-20260930.xsd#wdq_CommonClassDMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7eab-7c0e-beb2-2b8d4677a20c" xlink:to="loc_wdq_CommonClassDMember_01a17520-7eab-7c8a-bf29-7928810a53e1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RedeemablePreferredNoncontrollingInterestMember_01a17520-7eab-77c0-991e-24b09d85e5de" xlink:href="wdq-20260930.xsd#wdq_RedeemablePreferredNoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7eab-7c0e-beb2-2b8d4677a20c" xlink:to="loc_wdq_RedeemablePreferredNoncontrollingInterestMember_01a17520-7eab-77c0-991e-24b09d85e5de" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RedeemableNoncontrollingInterestMember_01a17520-7eab-7ac1-ada7-15ee0178045c" xlink:href="wdq-20260930.xsd#wdq_RedeemableNoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7eab-7c0e-beb2-2b8d4677a20c" xlink:to="loc_wdq_RedeemableNoncontrollingInterestMember_01a17520-7eab-7ac1-ada7-15ee0178045c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAxis_01a1c098-1819-7885-8208-4b260538226b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a17520-7eab-7b22-b1ff-4467ba441c14" xlink:to="loc_srt_RestatementAxis_01a1c098-1819-7885-8208-4b260538226b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_01a1c098-1819-7885-8208-4b260538226b_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RestatementAxis_01a1c098-1819-7885-8208-4b260538226b" xlink:to="loc_srt_RestatementDomain_01a1c098-1819-7885-8208-4b260538226b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_01a1c098-1819-7e53-a03b-6f5aba09fd2b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RestatementAxis_01a1c098-1819-7885-8208-4b260538226b" xlink:to="loc_srt_RestatementDomain_01a1c098-1819-7e53-a03b-6f5aba09fd2b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioPreviouslyReportedMember_01a1c098-6b64-73dd-b6b2-9d6c775cfddf" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioPreviouslyReportedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_01a1c098-1819-7e53-a03b-6f5aba09fd2b" xlink:to="loc_srt_ScenarioPreviouslyReportedMember_01a1c098-6b64-73dd-b6b2-9d6c775cfddf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RevisionOfPriorPeriodAccountingStandardsUpdateAdjustmentMember_01a1c098-a943-7099-ac46-309ba2815555" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RevisionOfPriorPeriodAccountingStandardsUpdateAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_01a1c098-1819-7e53-a03b-6f5aba09fd2b" xlink:to="loc_srt_RevisionOfPriorPeriodAccountingStandardsUpdateAdjustmentMember_01a1c098-a943-7099-ac46-309ba2815555" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a17520-7eab-7db1-b46b-c9ae9ed5e8e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7eab-7fd8-9a58-c89f7b5fa84b" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a17520-7eab-7db1-b46b-c9ae9ed5e8e6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_01a17520-7eab-71e7-bd17-3e6c6e57ef79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a17520-7eab-7db1-b46b-c9ae9ed5e8e6" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_01a17520-7eab-71e7-bd17-3e6c6e57ef79" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_01a17520-7eab-7ebd-b724-f428327ec6f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a17520-7eab-7db1-b46b-c9ae9ed5e8e6" xlink:to="loc_us-gaap_TreasuryStockCommonShares_01a17520-7eab-7ebd-b724-f428327ec6f6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_01a17520-7eab-7795-b306-6481a8d2951d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a17520-7eab-7db1-b46b-c9ae9ed5e8e6" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_01a17520-7eab-7795-b306-6481a8d2951d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossIncludingPortionAttributableToNonredeemableNoncontrollingInterest_01a17520-7eab-73d8-804d-3427089fd01c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossIncludingPortionAttributableToNonredeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a17520-7eab-7db1-b46b-c9ae9ed5e8e6" xlink:to="loc_us-gaap_NetIncomeLossIncludingPortionAttributableToNonredeemableNoncontrollingInterest_01a17520-7eab-73d8-804d-3427089fd01c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_01a17520-7eab-72fc-bb69-1d4577122187" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a17520-7eab-7db1-b46b-c9ae9ed5e8e6" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_01a17520-7eab-72fc-bb69-1d4577122187" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_01a17520-7eab-708b-9c64-4416a31f9650" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a17520-7eab-7db1-b46b-c9ae9ed5e8e6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_01a17520-7eab-708b-9c64-4416a31f9650" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_01a17520-7eab-7987-ba25-7ccf9e985f1c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a17520-7eab-7db1-b46b-c9ae9ed5e8e6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_01a17520-7eab-7987-ba25-7ccf9e985f1c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockSharesConverted1_01a17520-7eab-75b1-a85c-03078da8f284" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockSharesConverted1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a17520-7eab-7db1-b46b-c9ae9ed5e8e6" xlink:to="loc_us-gaap_ConversionOfStockSharesConverted1_01a17520-7eab-75b1-a85c-03078da8f284" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockAmountConverted1_01a17520-7eab-79f3-bc4e-5ebe02d4c2da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockAmountConverted1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a17520-7eab-7db1-b46b-c9ae9ed5e8e6" xlink:to="loc_us-gaap_ConversionOfStockAmountConverted1_01a17520-7eab-79f3-bc4e-5ebe02d4c2da" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_01a17520-7eab-74f8-ac1d-dc92025109b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a17520-7eab-7db1-b46b-c9ae9ed5e8e6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_01a17520-7eab-74f8-ac1d-dc92025109b8" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_01a17520-7eac-70ca-b834-9198b8141807" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a17520-7eab-7db1-b46b-c9ae9ed5e8e6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_01a17520-7eac-70ca-b834-9198b8141807" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_01a17520-7eac-79c6-a61f-66e1bc2fe4ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a17520-7eab-7db1-b46b-c9ae9ed5e8e6" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_01a17520-7eac-79c6-a61f-66e1bc2fe4ff" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_01a17520-7eac-725f-bb53-7201ac0cd3eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a17520-7eab-7db1-b46b-c9ae9ed5e8e6" xlink:to="loc_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_01a17520-7eac-725f-bb53-7201ac0cd3eb" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalIncreaseInCarryingAmountOfRedeemablePreferredStock_01a17520-7eac-791e-97cd-be828aad5c73" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalIncreaseInCarryingAmountOfRedeemablePreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a17520-7eab-7db1-b46b-c9ae9ed5e8e6" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalIncreaseInCarryingAmountOfRedeemablePreferredStock_01a17520-7eac-791e-97cd-be828aad5c73" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestIncreaseFromSaleOfParentEquityInterest_01a17520-7eac-7609-a89c-8cb394ae9d26" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoncontrollingInterestIncreaseFromSaleOfParentEquityInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a17520-7eab-7db1-b46b-c9ae9ed5e8e6" xlink:to="loc_us-gaap_NoncontrollingInterestIncreaseFromSaleOfParentEquityInterest_01a17520-7eac-7609-a89c-8cb394ae9d26" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseInCarryingAmountOfRedeemablePreferredStock_01a17520-7eac-7158-9ace-6446db14d96f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseInCarryingAmountOfRedeemablePreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a17520-7eab-7db1-b46b-c9ae9ed5e8e6" xlink:to="loc_us-gaap_IncreaseInCarryingAmountOfRedeemablePreferredStock_01a17520-7eac-7158-9ace-6446db14d96f" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_01a17520-7eac-7231-88d9-1d3229f50375" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_01a17520-7eac-7d64-8f4c-40a11e187579" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_01a17520-7eac-7369-96ca-29ca799f62e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_IncreaseDecreaseInTemporaryEquityAndRedeemableNoncontrollingInterestAbstract_01a17520-7eab-7c5e-94f1-eea4792ac871" xlink:href="wdq-20260930.xsd#wdq_IncreaseDecreaseInTemporaryEquityAndRedeemableNoncontrollingInterestAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7eab-7fd8-9a58-c89f7b5fa84b" xlink:to="loc_wdq_IncreaseDecreaseInTemporaryEquityAndRedeemableNoncontrollingInterestAbstract_01a17520-7eab-7c5e-94f1-eea4792ac871" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_01a17520-7eab-700d-88c8-d9adaf120123" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_IncreaseDecreaseInTemporaryEquityAndRedeemableNoncontrollingInterestAbstract_01a17520-7eab-7c5e-94f1-eea4792ac871" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_01a17520-7eab-700d-88c8-d9adaf120123" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityNetIncome_01a17520-7eab-76eb-858b-90924bd97d4e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityNetIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_IncreaseDecreaseInTemporaryEquityAndRedeemableNoncontrollingInterestAbstract_01a17520-7eab-7c5e-94f1-eea4792ac871" xlink:to="loc_us-gaap_TemporaryEquityNetIncome_01a17520-7eab-76eb-858b-90924bd97d4e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_OtherComprehensiveIncomeLossNetOfTaxAttributableToNonredeemableNoncontrollingInterest_01a17520-7eab-78db-ab62-170e7fb048d8" xlink:href="wdq-20260930.xsd#wdq_OtherComprehensiveIncomeLossNetOfTaxAttributableToNonredeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_IncreaseDecreaseInTemporaryEquityAndRedeemableNoncontrollingInterestAbstract_01a17520-7eab-7c5e-94f1-eea4792ac871" xlink:to="loc_wdq_OtherComprehensiveIncomeLossNetOfTaxAttributableToNonredeemableNoncontrollingInterest_01a17520-7eab-78db-ab62-170e7fb048d8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_TemporaryEquityIncreaseFromStockBasedCompensation_01a17520-7eab-721c-9533-3b6c4fdaf2c4" xlink:href="wdq-20260930.xsd#wdq_TemporaryEquityIncreaseFromStockBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_IncreaseDecreaseInTemporaryEquityAndRedeemableNoncontrollingInterestAbstract_01a17520-7eab-7c5e-94f1-eea4792ac871" xlink:to="loc_wdq_TemporaryEquityIncreaseFromStockBasedCompensation_01a17520-7eab-721c-9533-3b6c4fdaf2c4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment_01a17520-7eab-7722-8156-5556ea4b308c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_IncreaseDecreaseInTemporaryEquityAndRedeemableNoncontrollingInterestAbstract_01a17520-7eab-7c5e-94f1-eea4792ac871" xlink:to="loc_us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment_01a17520-7eab-7722-8156-5556ea4b308c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_TemporaryEquityIncreaseFromDividendDistribution_01a17520-7eab-78a1-885c-6a4fee28e6af" xlink:href="wdq-20260930.xsd#wdq_TemporaryEquityIncreaseFromDividendDistribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_IncreaseDecreaseInTemporaryEquityAndRedeemableNoncontrollingInterestAbstract_01a17520-7eab-7c5e-94f1-eea4792ac871" xlink:to="loc_wdq_TemporaryEquityIncreaseFromDividendDistribution_01a17520-7eab-78a1-885c-6a4fee28e6af" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues_01a17520-7eab-7d10-a8b2-05e02ada3a15" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_IncreaseDecreaseInTemporaryEquityAndRedeemableNoncontrollingInterestAbstract_01a17520-7eab-7c5e-94f1-eea4792ac871" xlink:to="loc_us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues_01a17520-7eab-7d10-a8b2-05e02ada3a15" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_TemporaryEquityRedemptionOfRedeemablePreferredNonControllingInterest_01a17520-7eab-7dab-9c53-61e7eb7ed366" xlink:href="wdq-20260930.xsd#wdq_TemporaryEquityRedemptionOfRedeemablePreferredNonControllingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_IncreaseDecreaseInTemporaryEquityAndRedeemableNoncontrollingInterestAbstract_01a17520-7eab-7c5e-94f1-eea4792ac871" xlink:to="loc_wdq_TemporaryEquityRedemptionOfRedeemablePreferredNonControllingInterest_01a17520-7eab-7dab-9c53-61e7eb7ed366" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityAccretionToRedemptionValue_01a17520-7eab-732e-993b-70f2a208ca4f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityAccretionToRedemptionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_IncreaseDecreaseInTemporaryEquityAndRedeemableNoncontrollingInterestAbstract_01a17520-7eab-7c5e-94f1-eea4792ac871" xlink:to="loc_us-gaap_TemporaryEquityAccretionToRedemptionValue_01a17520-7eab-732e-993b-70f2a208ca4f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_01a17520-7eab-7345-a46b-a9cca68ee895" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSParenthetical" xlink:type="simple" xlink:href="wdq-20260930.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSParenthetical"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a17520-7eac-7855-96db-cce5a7da3d75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_01a17520-7eac-7ad1-8f5e-d5ac7923eb98" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7eac-7855-96db-cce5a7da3d75" xlink:to="loc_us-gaap_StatementTable_01a17520-7eac-7ad1-8f5e-d5ac7923eb98" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7eac-7341-8df7-39d1df7c0909" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a17520-7eac-7ad1-8f5e-d5ac7923eb98" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7eac-7341-8df7-39d1df7c0909" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a17520-7eac-7341-8df7-39d1df7c0909_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7eac-7341-8df7-39d1df7c0909" xlink:to="loc_us-gaap_RelatedPartyDomain_01a17520-7eac-7341-8df7-39d1df7c0909_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a17520-7eac-73e0-b69b-068d740e6f3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7eac-7341-8df7-39d1df7c0909" xlink:to="loc_us-gaap_RelatedPartyDomain_01a17520-7eac-73e0-b69b-068d740e6f3f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a17520-7eac-7d0d-97a4-de161dc84d99" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a17520-7eac-73e0-b69b-068d740e6f3f" xlink:to="loc_us-gaap_RelatedPartyMember_01a17520-7eac-7d0d-97a4-de161dc84d99" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_01a17520-7eac-79af-b0c8-029f27ff58bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7eac-7855-96db-cce5a7da3d75" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_01a17520-7eac-79af-b0c8-029f27ff58bb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherAccountsPayable_01a17520-7eac-7f93-8149-7397a2027e85" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOtherAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7eac-7855-96db-cce5a7da3d75" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherAccountsPayable_01a17520-7eac-7f93-8149-7397a2027e85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPaidCapitalized_01a1bcec-ee7c-7e91-ba9a-6ecd1211e7a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestPaidCapitalized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a17520-7eac-7855-96db-cce5a7da3d75" xlink:to="loc_us-gaap_InterestPaidCapitalized_01a1bcec-ee7c-7e91-ba9a-6ecd1211e7a3" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_01a17520-7eac-763b-82f3-63682813566c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_us-gaap_DerivativeTable_01a17520-7eac-763b-82f3-63682813566c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7eac-738d-8ea4-0e2848cb572d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a17520-7eac-763b-82f3-63682813566c" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7eac-738d-8ea4-0e2848cb572d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a17520-7eac-738d-8ea4-0e2848cb572d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7eac-738d-8ea4-0e2848cb572d" xlink:to="loc_us-gaap_SegmentDomain_01a17520-7eac-738d-8ea4-0e2848cb572d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a17520-7eac-7cd9-807d-5423f7c5f3b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7eac-738d-8ea4-0e2848cb572d" xlink:to="loc_us-gaap_SegmentDomain_01a17520-7eac-7cd9-807d-5423f7c5f3b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_FuelStationServicesSegmentMember_01a17520-7eac-79f6-ae1b-55ec604a44b2" xlink:href="wdq-20260930.xsd#wdq_FuelStationServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a17520-7eac-7cd9-807d-5423f7c5f3b6" xlink:to="loc_wdq_FuelStationServicesSegmentMember_01a17520-7eac-79f6-ae1b-55ec604a44b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RenewablePowerSegmentMember_01a17520-7eac-70d9-a8b8-f825df2c0d4e" xlink:href="wdq-20260930.xsd#wdq_RenewablePowerSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a17520-7eac-7cd9-807d-5423f7c5f3b6" xlink:to="loc_wdq_RenewablePowerSegmentMember_01a17520-7eac-70d9-a8b8-f825df2c0d4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_01a17520-7eac-7568-9aa4-92203ea7f9f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a17520-7eac-763b-82f3-63682813566c" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_01a17520-7eac-7568-9aa4-92203ea7f9f2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_01a17520-7eac-7998-b2dd-4ba680f5aea1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a17520-7eac-763b-82f3-63682813566c" xlink:to="loc_srt_MajorCustomersAxis_01a17520-7eac-7998-b2dd-4ba680f5aea1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_01a17520-7eac-7998-b2dd-4ba680f5aea1_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_01a17520-7eac-7998-b2dd-4ba680f5aea1" xlink:to="loc_srt_NameOfMajorCustomerDomain_01a17520-7eac-7998-b2dd-4ba680f5aea1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_01a17520-7eac-7e82-8547-7cd5b8d133e8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_01a17520-7eac-7998-b2dd-4ba680f5aea1" xlink:to="loc_srt_NameOfMajorCustomerDomain_01a17520-7eac-7e82-8547-7cd5b8d133e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_TwoCustomerMember_01a17520-7eac-7a64-8f70-8426501972d2" xlink:href="wdq-20260930.xsd#wdq_TwoCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_01a17520-7eac-7e82-8547-7cd5b8d133e8" xlink:to="loc_wdq_TwoCustomerMember_01a17520-7eac-7a64-8f70-8426501972d2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_FourCustomersMember_01a17520-7eac-7e22-a71d-66b5add73ab8" xlink:href="wdq-20260930.xsd#wdq_FourCustomersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_01a17520-7eac-7e82-8547-7cd5b8d133e8" xlink:to="loc_wdq_FourCustomersMember_01a17520-7eac-7e22-a71d-66b5add73ab8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a17520-7eac-714a-876d-6f375b4e5d05" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a17520-7eac-763b-82f3-63682813566c" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a17520-7eac-714a-876d-6f375b4e5d05" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a17520-7eac-714a-876d-6f375b4e5d05_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a17520-7eac-714a-876d-6f375b4e5d05" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a17520-7eac-714a-876d-6f375b4e5d05_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a17520-7eac-7af1-a0ec-090656a854d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a17520-7eac-714a-876d-6f375b4e5d05" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a17520-7eac-7af1-a0ec-090656a854d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_01a17520-7eac-735e-abea-f0093e06fd30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a17520-7eac-7af1-a0ec-090656a854d4" xlink:to="loc_us-gaap_SalesRevenueNetMember_01a17520-7eac-735e-abea-f0093e06fd30" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableMember_01a17520-7eac-7859-ae08-2f6a08524e1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a17520-7eac-7af1-a0ec-090656a854d4" xlink:to="loc_us-gaap_AccountsPayableMember_01a17520-7eac-7859-ae08-2f6a08524e1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_01a17520-7eac-7a4e-b989-14f679de30d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a17520-7eac-763b-82f3-63682813566c" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_01a17520-7eac-7a4e-b989-14f679de30d9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a17520-7eac-7a4e-b989-14f679de30d9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a17520-7eac-7a4e-b989-14f679de30d9" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a17520-7eac-7a4e-b989-14f679de30d9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a17520-7eac-7950-8d5b-5397784ae214" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a17520-7eac-7a4e-b989-14f679de30d9" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a17520-7eac-7950-8d5b-5397784ae214" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_01a17520-7eac-7751-9158-4b2cb03f798c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_01a17520-7eac-7950-8d5b-5397784ae214" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_01a17520-7eac-7751-9158-4b2cb03f798c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplierConcentrationRiskMember_01a17520-7eac-7d44-a85f-f88dd32f44b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SupplierConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_01a17520-7eac-7950-8d5b-5397784ae214" xlink:to="loc_us-gaap_SupplierConcentrationRiskMember_01a17520-7eac-7d44-a85f-f88dd32f44b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_01a17520-7eac-73bb-a3cb-54ed9a1337f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a17520-7eac-763b-82f3-63682813566c" xlink:to="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_01a17520-7eac-73bb-a3cb-54ed9a1337f2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_01a17520-7eac-73bb-a3cb-54ed9a1337f2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_01a17520-7eac-73bb-a3cb-54ed9a1337f2" xlink:to="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_01a17520-7eac-73bb-a3cb-54ed9a1337f2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_01a17520-7eac-726a-8261-d83b75e5c10f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_01a17520-7eac-73bb-a3cb-54ed9a1337f2" xlink:to="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_01a17520-7eac-726a-8261-d83b75e5c10f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_OneSupplierMember_01a17520-7eac-7ed4-ad7c-ba1f71514840" xlink:href="wdq-20260930.xsd#wdq_OneSupplierMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_01a17520-7eac-726a-8261-d83b75e5c10f" xlink:to="loc_wdq_OneSupplierMember_01a17520-7eac-7ed4-ad7c-ba1f71514840" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a1c192-3df7-7ae6-a13b-05c948e1fedb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a17520-7eac-763b-82f3-63682813566c" xlink:to="loc_srt_RangeAxis_01a1c192-3df7-7ae6-a13b-05c948e1fedb" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a1c192-3df7-7ae6-a13b-05c948e1fedb_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_01a1c192-3df7-7ae6-a13b-05c948e1fedb" xlink:to="loc_srt_RangeMember_01a1c192-3df7-7ae6-a13b-05c948e1fedb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a1c192-3df7-73b2-a7b5-71ed01b6b132" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_01a1c192-3df7-7ae6-a13b-05c948e1fedb" xlink:to="loc_srt_RangeMember_01a1c192-3df7-73b2-a7b5-71ed01b6b132" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a1c192-3df7-7799-b3fd-29f4af6d42f3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a1c192-3df7-73b2-a7b5-71ed01b6b132" xlink:to="loc_srt_MaximumMember_01a1c192-3df7-7799-b3fd-29f4af6d42f3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAxis_01a1c192-3df7-7538-b7b2-3df692fd02e2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a17520-7eac-763b-82f3-63682813566c" xlink:to="loc_srt_RestatementAxis_01a1c192-3df7-7538-b7b2-3df692fd02e2" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_01a1c192-3df7-7538-b7b2-3df692fd02e2_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RestatementAxis_01a1c192-3df7-7538-b7b2-3df692fd02e2" xlink:to="loc_srt_RestatementDomain_01a1c192-3df7-7538-b7b2-3df692fd02e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_01a1c192-3df7-7ef6-8cca-c6bed371d5bf" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RestatementAxis_01a1c192-3df7-7538-b7b2-3df692fd02e2" xlink:to="loc_srt_RestatementDomain_01a1c192-3df7-7ef6-8cca-c6bed371d5bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAdjustmentMember_01a1c192-3df7-76dc-8609-3d19342e134c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_01a1c192-3df7-7ef6-8cca-c6bed371d5bf" xlink:to="loc_srt_RestatementAdjustmentMember_01a1c192-3df7-76dc-8609-3d19342e134c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_01a1a575-cfd5-7709-add2-513f00f9ee3e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_01a1a575-cfd5-7709-add2-513f00f9ee3e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_01a1a9c2-ffc2-7932-be91-2536041c9750" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_us-gaap_EquityMethodInvestments_01a1a9c2-ffc2-7932-be91-2536041c9750" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_SellingGeneralAndAdministrativeExpenseAmountOverstated_01a1accd-3a69-7943-9aa0-992b76bdcda0" xlink:href="wdq-20260930.xsd#wdq_SellingGeneralAndAdministrativeExpenseAmountOverstated"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_wdq_SellingGeneralAndAdministrativeExpenseAmountOverstated_01a1accd-3a69-7943-9aa0-992b76bdcda0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_CostOfProductAndServiceSoldAmountUnderstated_01a1accd-4eb6-72f3-a681-ac659760af7c" xlink:href="wdq-20260930.xsd#wdq_CostOfProductAndServiceSoldAmountUnderstated"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_wdq_CostOfProductAndServiceSoldAmountUnderstated_01a1accd-4eb6-72f3-a681-ac659760af7c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_EnvironmentalCreditsHeldForSaleCurrent_01a17520-7eac-74bd-944b-0f8f8e841667" xlink:href="wdq-20260930.xsd#wdq_EnvironmentalCreditsHeldForSaleCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_wdq_EnvironmentalCreditsHeldForSaleCurrent_01a17520-7eac-74bd-944b-0f8f8e841667" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_ContractWithCustomerAssetAfterAllowanceForCreditLossCostAndEstimatedEarningsInExcessOfBillingsCurrent_01a17520-7eac-7dbd-8428-cd4f43fec40b" xlink:href="wdq-20260930.xsd#wdq_ContractWithCustomerAssetAfterAllowanceForCreditLossCostAndEstimatedEarningsInExcessOfBillingsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_wdq_ContractWithCustomerAssetAfterAllowanceForCreditLossCostAndEstimatedEarningsInExcessOfBillingsCurrent_01a17520-7eac-7dbd-8428-cd4f43fec40b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_01a17520-7eac-7059-9126-980e32144a64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_01a17520-7eac-7059-9126-980e32144a64" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_01a17520-7eac-7583-8ae9-e5de7ff7dec2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ImpairmentOfLongLivedAssetsHeldForUse"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_01a17520-7eac-7583-8ae9-e5de7ff7dec2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_01a17520-7eac-779c-9fce-3d5013dbaaa8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_01a17520-7eac-779c-9fce-3d5013dbaaa8" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_01a17520-7eac-7c6d-8590-16b50fdec545" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_01a17520-7eac-7c6d-8590-16b50fdec545" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_01a17520-7eac-7b95-8fbe-d76ca57b2060" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_01a17520-7eac-7b95-8fbe-d76ca57b2060" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails_1" xlink:type="simple" xlink:href="wdq-20260930.xsd#SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_01a17520-7eac-763b-82f3-63682813566c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_us-gaap_DerivativeTable_01a17520-7eac-763b-82f3-63682813566c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7eac-738d-8ea4-0e2848cb572d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a17520-7eac-763b-82f3-63682813566c" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7eac-738d-8ea4-0e2848cb572d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a17520-7eac-738d-8ea4-0e2848cb572d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7eac-738d-8ea4-0e2848cb572d" xlink:to="loc_us-gaap_SegmentDomain_01a17520-7eac-738d-8ea4-0e2848cb572d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a17520-7eac-7cd9-807d-5423f7c5f3b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7eac-738d-8ea4-0e2848cb572d" xlink:to="loc_us-gaap_SegmentDomain_01a17520-7eac-7cd9-807d-5423f7c5f3b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_FuelStationServicesSegmentMember_01a17520-7eac-79f6-ae1b-55ec604a44b2" xlink:href="wdq-20260930.xsd#wdq_FuelStationServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a17520-7eac-7cd9-807d-5423f7c5f3b6" xlink:to="loc_wdq_FuelStationServicesSegmentMember_01a17520-7eac-79f6-ae1b-55ec604a44b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RenewablePowerSegmentMember_01a17520-7eac-70d9-a8b8-f825df2c0d4e" xlink:href="wdq-20260930.xsd#wdq_RenewablePowerSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a17520-7eac-7cd9-807d-5423f7c5f3b6" xlink:to="loc_wdq_RenewablePowerSegmentMember_01a17520-7eac-70d9-a8b8-f825df2c0d4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_01a17520-7eac-7998-b2dd-4ba680f5aea1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a17520-7eac-763b-82f3-63682813566c" xlink:to="loc_srt_MajorCustomersAxis_01a17520-7eac-7998-b2dd-4ba680f5aea1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_01a17520-7eac-7998-b2dd-4ba680f5aea1_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_01a17520-7eac-7998-b2dd-4ba680f5aea1" xlink:to="loc_srt_NameOfMajorCustomerDomain_01a17520-7eac-7998-b2dd-4ba680f5aea1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_01a17520-7eac-7e82-8547-7cd5b8d133e8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_01a17520-7eac-7998-b2dd-4ba680f5aea1" xlink:to="loc_srt_NameOfMajorCustomerDomain_01a17520-7eac-7e82-8547-7cd5b8d133e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_TwoCustomerMember_01a17520-7eac-7a64-8f70-8426501972d2" xlink:href="wdq-20260930.xsd#wdq_TwoCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_01a17520-7eac-7e82-8547-7cd5b8d133e8" xlink:to="loc_wdq_TwoCustomerMember_01a17520-7eac-7a64-8f70-8426501972d2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_FourCustomersMember_01a17520-7eac-7e22-a71d-66b5add73ab8" xlink:href="wdq-20260930.xsd#wdq_FourCustomersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_01a17520-7eac-7e82-8547-7cd5b8d133e8" xlink:to="loc_wdq_FourCustomersMember_01a17520-7eac-7e22-a71d-66b5add73ab8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a17520-7eac-714a-876d-6f375b4e5d05" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a17520-7eac-763b-82f3-63682813566c" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a17520-7eac-714a-876d-6f375b4e5d05" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a17520-7eac-714a-876d-6f375b4e5d05_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a17520-7eac-714a-876d-6f375b4e5d05" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a17520-7eac-714a-876d-6f375b4e5d05_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a17520-7eac-7af1-a0ec-090656a854d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a17520-7eac-714a-876d-6f375b4e5d05" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a17520-7eac-7af1-a0ec-090656a854d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_01a17520-7eac-735e-abea-f0093e06fd30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a17520-7eac-7af1-a0ec-090656a854d4" xlink:to="loc_us-gaap_SalesRevenueNetMember_01a17520-7eac-735e-abea-f0093e06fd30" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableMember_01a17520-7eac-7859-ae08-2f6a08524e1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a17520-7eac-7af1-a0ec-090656a854d4" xlink:to="loc_us-gaap_AccountsPayableMember_01a17520-7eac-7859-ae08-2f6a08524e1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_01a17520-7eac-7a4e-b989-14f679de30d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a17520-7eac-763b-82f3-63682813566c" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_01a17520-7eac-7a4e-b989-14f679de30d9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a17520-7eac-7a4e-b989-14f679de30d9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a17520-7eac-7a4e-b989-14f679de30d9" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a17520-7eac-7a4e-b989-14f679de30d9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a17520-7eac-7950-8d5b-5397784ae214" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a17520-7eac-7a4e-b989-14f679de30d9" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a17520-7eac-7950-8d5b-5397784ae214" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_01a17520-7eac-7751-9158-4b2cb03f798c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_01a17520-7eac-7950-8d5b-5397784ae214" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_01a17520-7eac-7751-9158-4b2cb03f798c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplierConcentrationRiskMember_01a17520-7eac-7d44-a85f-f88dd32f44b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SupplierConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_01a17520-7eac-7950-8d5b-5397784ae214" xlink:to="loc_us-gaap_SupplierConcentrationRiskMember_01a17520-7eac-7d44-a85f-f88dd32f44b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_01a17520-7eac-73bb-a3cb-54ed9a1337f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a17520-7eac-763b-82f3-63682813566c" xlink:to="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_01a17520-7eac-73bb-a3cb-54ed9a1337f2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_01a17520-7eac-73bb-a3cb-54ed9a1337f2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_01a17520-7eac-73bb-a3cb-54ed9a1337f2" xlink:to="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_01a17520-7eac-73bb-a3cb-54ed9a1337f2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_01a17520-7eac-726a-8261-d83b75e5c10f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis_01a17520-7eac-73bb-a3cb-54ed9a1337f2" xlink:to="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_01a17520-7eac-726a-8261-d83b75e5c10f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_OneSupplierMember_01a17520-7eac-7ed4-ad7c-ba1f71514840" xlink:href="wdq-20260930.xsd#wdq_OneSupplierMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionSupplierDomain_01a17520-7eac-726a-8261-d83b75e5c10f" xlink:to="loc_wdq_OneSupplierMember_01a17520-7eac-7ed4-ad7c-ba1f71514840" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a1c192-3df7-7ae6-a13b-05c948e1fedb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a17520-7eac-763b-82f3-63682813566c" xlink:to="loc_srt_RangeAxis_01a1c192-3df7-7ae6-a13b-05c948e1fedb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a1c192-3df7-7ae6-a13b-05c948e1fedb_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_01a1c192-3df7-7ae6-a13b-05c948e1fedb" xlink:to="loc_srt_RangeMember_01a1c192-3df7-7ae6-a13b-05c948e1fedb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a1c192-3df7-73b2-a7b5-71ed01b6b132" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_01a1c192-3df7-7ae6-a13b-05c948e1fedb" xlink:to="loc_srt_RangeMember_01a1c192-3df7-73b2-a7b5-71ed01b6b132" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a1c192-3df7-7799-b3fd-29f4af6d42f3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a1c192-3df7-73b2-a7b5-71ed01b6b132" xlink:to="loc_srt_MaximumMember_01a1c192-3df7-7799-b3fd-29f4af6d42f3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAxis_01a1c192-3df7-7538-b7b2-3df692fd02e2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a17520-7eac-763b-82f3-63682813566c" xlink:to="loc_srt_RestatementAxis_01a1c192-3df7-7538-b7b2-3df692fd02e2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_01a1c192-3df7-7538-b7b2-3df692fd02e2_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RestatementAxis_01a1c192-3df7-7538-b7b2-3df692fd02e2" xlink:to="loc_srt_RestatementDomain_01a1c192-3df7-7538-b7b2-3df692fd02e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_01a1c192-3df7-7ef6-8cca-c6bed371d5bf" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RestatementAxis_01a1c192-3df7-7538-b7b2-3df692fd02e2" xlink:to="loc_srt_RestatementDomain_01a1c192-3df7-7ef6-8cca-c6bed371d5bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAdjustmentMember_01a1c192-3df7-76dc-8609-3d19342e134c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_01a1c192-3df7-7ef6-8cca-c6bed371d5bf" xlink:to="loc_srt_RestatementAdjustmentMember_01a1c192-3df7-76dc-8609-3d19342e134c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_01a1a575-cfd5-7709-add2-513f00f9ee3e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_01a1a575-cfd5-7709-add2-513f00f9ee3e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_01a1a9c2-ffc2-7932-be91-2536041c9750" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_us-gaap_EquityMethodInvestments_01a1a9c2-ffc2-7932-be91-2536041c9750" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_SellingGeneralAndAdministrativeExpenseAmountOverstated_01a1accd-3a69-7943-9aa0-992b76bdcda0" xlink:href="wdq-20260930.xsd#wdq_SellingGeneralAndAdministrativeExpenseAmountOverstated"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_wdq_SellingGeneralAndAdministrativeExpenseAmountOverstated_01a1accd-3a69-7943-9aa0-992b76bdcda0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_CostOfProductAndServiceSoldAmountUnderstated_01a1accd-4eb6-72f3-a681-ac659760af7c" xlink:href="wdq-20260930.xsd#wdq_CostOfProductAndServiceSoldAmountUnderstated"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_wdq_CostOfProductAndServiceSoldAmountUnderstated_01a1accd-4eb6-72f3-a681-ac659760af7c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_EnvironmentalCreditsHeldForSaleCurrent_01a17520-7eac-74bd-944b-0f8f8e841667" xlink:href="wdq-20260930.xsd#wdq_EnvironmentalCreditsHeldForSaleCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_wdq_EnvironmentalCreditsHeldForSaleCurrent_01a17520-7eac-74bd-944b-0f8f8e841667" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_ContractWithCustomerAssetAfterAllowanceForCreditLossCostAndEstimatedEarningsInExcessOfBillingsCurrent_01a17520-7eac-7dbd-8428-cd4f43fec40b" xlink:href="wdq-20260930.xsd#wdq_ContractWithCustomerAssetAfterAllowanceForCreditLossCostAndEstimatedEarningsInExcessOfBillingsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_wdq_ContractWithCustomerAssetAfterAllowanceForCreditLossCostAndEstimatedEarningsInExcessOfBillingsCurrent_01a17520-7eac-7dbd-8428-cd4f43fec40b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_01a17520-7eac-7059-9126-980e32144a64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_01a17520-7eac-7059-9126-980e32144a64" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_01a17520-7eac-7583-8ae9-e5de7ff7dec2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ImpairmentOfLongLivedAssetsHeldForUse"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_01a17520-7eac-7583-8ae9-e5de7ff7dec2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_01a17520-7eac-779c-9fce-3d5013dbaaa8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_01a17520-7eac-779c-9fce-3d5013dbaaa8" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_01a17520-7eac-7c6d-8590-16b50fdec545" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_01a17520-7eac-7c6d-8590-16b50fdec545" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_01a17520-7eac-7b95-8fbe-d76ca57b2060" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7eac-7ecc-9423-08c3ffed7a8a" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_01a17520-7eac-7b95-8fbe-d76ca57b2060" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofCondensedConsolidatedStatementsofOperationsDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofCondensedConsolidatedStatementsofOperationsDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofCondensedConsolidatedStatementsofOperationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a579-e999-7c7e-b52c-f5aa872ff391" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfErrorCorrectionsAndPriorPeriodAdjustmentRestatementTable_01a1a579-e999-74bf-9863-2f9fe8b458f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfErrorCorrectionsAndPriorPeriodAdjustmentRestatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a579-e999-7c7e-b52c-f5aa872ff391" xlink:to="loc_us-gaap_ScheduleOfErrorCorrectionsAndPriorPeriodAdjustmentRestatementTable_01a1a579-e999-74bf-9863-2f9fe8b458f7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAxis_01a1a579-e999-7570-8f18-d628d0b6006c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfErrorCorrectionsAndPriorPeriodAdjustmentRestatementTable_01a1a579-e999-74bf-9863-2f9fe8b458f7" xlink:to="loc_srt_RestatementAxis_01a1a579-e999-7570-8f18-d628d0b6006c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_01a1a579-e999-7570-8f18-d628d0b6006c_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RestatementAxis_01a1a579-e999-7570-8f18-d628d0b6006c" xlink:to="loc_srt_RestatementDomain_01a1a579-e999-7570-8f18-d628d0b6006c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_01a1a579-e999-727e-ae94-f2ad5213a233" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RestatementAxis_01a1a579-e999-7570-8f18-d628d0b6006c" xlink:to="loc_srt_RestatementDomain_01a1a579-e999-727e-ae94-f2ad5213a233" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioPreviouslyReportedMember_01a1af92-51db-7c44-a3ec-9de3e515ec21" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioPreviouslyReportedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_01a1a579-e999-727e-ae94-f2ad5213a233" xlink:to="loc_srt_ScenarioPreviouslyReportedMember_01a1af92-51db-7c44-a3ec-9de3e515ec21" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAdjustmentMember_01a1af93-70a8-70e0-b220-dadbca81a373" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_01a1a579-e999-727e-ae94-f2ad5213a233" xlink:to="loc_srt_RestatementAdjustmentMember_01a1af93-70a8-70e0-b220-dadbca81a373" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a1af8d-aa95-7cb6-bfd4-90011a7396a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfErrorCorrectionsAndPriorPeriodAdjustmentRestatementTable_01a1a579-e999-74bf-9863-2f9fe8b458f7" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a1af8d-aa95-7cb6-bfd4-90011a7396a0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a1af8d-aa95-7cb6-bfd4-90011a7396a0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a1af8d-aa95-7cb6-bfd4-90011a7396a0" xlink:to="loc_us-gaap_SegmentDomain_01a1af8d-aa95-7cb6-bfd4-90011a7396a0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a1af8d-aa95-7a57-a6fa-89095fa1b5ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a1af8d-aa95-7cb6-bfd4-90011a7396a0" xlink:to="loc_us-gaap_SegmentDomain_01a1af8d-aa95-7a57-a6fa-89095fa1b5ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RenewableNaturalGasFuelSupplySegmentMember_01a1af8d-aa95-73e9-9228-f0833f711508" xlink:href="wdq-20260930.xsd#wdq_RenewableNaturalGasFuelSupplySegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a1af8d-aa95-7a57-a6fa-89095fa1b5ee" xlink:to="loc_wdq_RenewableNaturalGasFuelSupplySegmentMember_01a1af8d-aa95-73e9-9228-f0833f711508" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a1bdbc-c5ed-77a6-ae33-517e029ec279" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfErrorCorrectionsAndPriorPeriodAdjustmentRestatementTable_01a1a579-e999-74bf-9863-2f9fe8b458f7" xlink:to="loc_srt_RangeAxis_01a1bdbc-c5ed-77a6-ae33-517e029ec279" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a1bdbc-c5ed-77a6-ae33-517e029ec279_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_01a1bdbc-c5ed-77a6-ae33-517e029ec279" xlink:to="loc_srt_RangeMember_01a1bdbc-c5ed-77a6-ae33-517e029ec279_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a1bdbc-c5ed-78d1-b401-f60eaccf1449" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_01a1bdbc-c5ed-77a6-ae33-517e029ec279" xlink:to="loc_srt_RangeMember_01a1bdbc-c5ed-78d1-b401-f60eaccf1449" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a1bdbc-dd31-7b0a-bfc5-e5f4f9b43061" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a1bdbc-c5ed-78d1-b401-f60eaccf1449" xlink:to="loc_srt_MaximumMember_01a1bdbc-dd31-7b0a-bfc5-e5f4f9b43061" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_01a1af8d-aa95-7d48-a025-a901f9199ae7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a579-e999-7c7e-b52c-f5aa872ff391" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_01a1af8d-aa95-7d48-a025-a901f9199ae7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_01a1af86-e79d-740a-bc43-667fa59551be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a579-e999-7c7e-b52c-f5aa872ff391" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_01a1af86-e79d-740a-bc43-667fa59551be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAmortizationAndAccretionNet_01a1af86-e79d-706b-a27d-9df1eed7b96b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationAmortizationAndAccretionNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a579-e999-7c7e-b52c-f5aa872ff391" xlink:to="loc_us-gaap_DepreciationAmortizationAndAccretionNet_01a1af86-e79d-706b-a27d-9df1eed7b96b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_01a1af86-e79d-70d7-aa78-fbf3c81b0597" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a579-e999-7c7e-b52c-f5aa872ff391" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_01a1af86-e79d-70d7-aa78-fbf3c81b0597" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_01a1af86-0fe6-7242-9379-65dba6efaed7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a579-e999-7c7e-b52c-f5aa872ff391" xlink:to="loc_us-gaap_CostsAndExpenses_01a1af86-0fe6-7242-9379-65dba6efaed7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_01a1af86-e79d-70f7-8cdb-3c443855972e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a579-e999-7c7e-b52c-f5aa872ff391" xlink:to="loc_us-gaap_OperatingIncomeLoss_01a1af86-e79d-70f7-8cdb-3c443855972e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a1af86-e79d-73f8-a458-2568f08931a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a579-e999-7c7e-b52c-f5aa872ff391" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a1af86-e79d-73f8-a458-2568f08931a0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_01a1af86-e79d-788f-9299-c0ddec002f8d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a579-e999-7c7e-b52c-f5aa872ff391" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_01a1af86-e79d-788f-9299-c0ddec002f8d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_01a1af86-e79d-7713-99cc-ee117eef1320" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a579-e999-7c7e-b52c-f5aa872ff391" xlink:to="loc_us-gaap_ProfitLoss_01a1af86-e79d-7713-99cc-ee117eef1320" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_01a1af86-e79d-7fc7-ad75-6afb13f0f15e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a579-e999-7c7e-b52c-f5aa872ff391" xlink:to="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_01a1af86-e79d-7fc7-ad75-6afb13f0f15e" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_01a1af86-e79d-7b76-8688-24acf6a0b60f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a579-e999-7c7e-b52c-f5aa872ff391" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_01a1af86-e79d-7b76-8688-24acf6a0b60f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_01a1c14b-868a-7cd9-8619-116fd3d47081" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a579-e999-7c7e-b52c-f5aa872ff391" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_01a1c14b-868a-7cd9-8619-116fd3d47081" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareAbstract_01a1a57c-1931-768d-a8c5-c6f2f3e32593" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a579-e999-7c7e-b52c-f5aa872ff391" xlink:to="loc_us-gaap_EarningsPerShareAbstract_01a1a57c-1931-768d-a8c5-c6f2f3e32593" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_01a1a579-e999-75fe-9f36-75b61f6a24dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_01a1a57c-1931-768d-a8c5-c6f2f3e32593" xlink:to="loc_us-gaap_EarningsPerShareBasic_01a1a579-e999-75fe-9f36-75b61f6a24dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_01a1a579-e999-7f0f-872b-fdd5542c6a72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_01a1a57c-1931-768d-a8c5-c6f2f3e32593" xlink:to="loc_us-gaap_EarningsPerShareDiluted_01a1a579-e999-7f0f-872b-fdd5542c6a72" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofCondensedConsolidatedBalanceSheetsDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofCondensedConsolidatedBalanceSheetsDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofCondensedConsolidatedBalanceSheetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a57d-c93e-7049-b6ee-20918cdef85f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfErrorCorrectionsAndPriorPeriodAdjustmentRestatementTable_01a1a57d-c93e-787e-a300-44b720b041d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfErrorCorrectionsAndPriorPeriodAdjustmentRestatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a57d-c93e-7049-b6ee-20918cdef85f" xlink:to="loc_us-gaap_ScheduleOfErrorCorrectionsAndPriorPeriodAdjustmentRestatementTable_01a1a57d-c93e-787e-a300-44b720b041d3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAxis_01a1a57d-c93e-7106-8a81-ddf421dfbc44" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfErrorCorrectionsAndPriorPeriodAdjustmentRestatementTable_01a1a57d-c93e-787e-a300-44b720b041d3" xlink:to="loc_srt_RestatementAxis_01a1a57d-c93e-7106-8a81-ddf421dfbc44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_01a1a57d-c93e-7106-8a81-ddf421dfbc44_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RestatementAxis_01a1a57d-c93e-7106-8a81-ddf421dfbc44" xlink:to="loc_srt_RestatementDomain_01a1a57d-c93e-7106-8a81-ddf421dfbc44_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_01a1a57d-c93e-7c7d-8687-467ffbe41c03" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RestatementAxis_01a1a57d-c93e-7106-8a81-ddf421dfbc44" xlink:to="loc_srt_RestatementDomain_01a1a57d-c93e-7c7d-8687-467ffbe41c03" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioPreviouslyReportedMember_01a1afb1-769b-73e3-beff-f3966e851d5c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioPreviouslyReportedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_01a1a57d-c93e-7c7d-8687-467ffbe41c03" xlink:to="loc_srt_ScenarioPreviouslyReportedMember_01a1afb1-769b-73e3-beff-f3966e851d5c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAdjustmentMember_01a1afb1-769b-72a9-b3bb-5de136c8b733" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_01a1a57d-c93e-7c7d-8687-467ffbe41c03" xlink:to="loc_srt_RestatementAdjustmentMember_01a1afb1-769b-72a9-b3bb-5de136c8b733" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrantsReceivableCurrent_01a1a57d-c93e-787b-9439-ffda02de1de0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GrantsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a57d-c93e-7049-b6ee-20918cdef85f" xlink:to="loc_us-gaap_GrantsReceivableCurrent_01a1a57d-c93e-787b-9439-ffda02de1de0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_01a1a57d-c93e-7369-9381-9470675c109e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a57d-c93e-7049-b6ee-20918cdef85f" xlink:to="loc_us-gaap_AssetsCurrent_01a1a57d-c93e-7369-9381-9470675c109e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_01a1a57d-c93e-7314-bd7c-81df851b2cb5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a57d-c93e-7049-b6ee-20918cdef85f" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_01a1a57d-c93e-7314-bd7c-81df851b2cb5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_01a1a57d-c93e-7b82-9350-2de47306c9b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a57d-c93e-7049-b6ee-20918cdef85f" xlink:to="loc_us-gaap_EquityMethodInvestments_01a1a57d-c93e-7b82-9350-2de47306c9b3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_01a1a57d-c93e-71a2-a85f-2f9c7a36495c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a57d-c93e-7049-b6ee-20918cdef85f" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_01a1a57d-c93e-71a2-a85f-2f9c7a36495c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_01a1a57d-c93e-78eb-93bd-4b8f88a786a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a57d-c93e-7049-b6ee-20918cdef85f" xlink:to="loc_us-gaap_Assets_01a1a57d-c93e-78eb-93bd-4b8f88a786a3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAccruedLiabilitiesCurrent_01a1a57d-c93e-722b-b378-2edb4051ebe8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a57d-c93e-7049-b6ee-20918cdef85f" xlink:to="loc_us-gaap_OtherAccruedLiabilitiesCurrent_01a1a57d-c93e-722b-b378-2edb4051ebe8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_01a1af9b-93ec-7edc-8beb-21a4f5361ed3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a57d-c93e-7049-b6ee-20918cdef85f" xlink:to="loc_us-gaap_Liabilities_01a1af9b-93ec-7edc-8beb-21a4f5361ed3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_01a1a57d-c93e-7d9e-af83-268eed3a4cd0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a57d-c93e-7049-b6ee-20918cdef85f" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_01a1a57d-c93e-7d9e-af83-268eed3a4cd0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a1a57d-c93e-7d2a-ad89-a69275dab13a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a57d-c93e-7049-b6ee-20918cdef85f" xlink:to="loc_us-gaap_StockholdersEquity_01a1a57d-c93e-7d2a-ad89-a69275dab13a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_01a1a57d-c93e-7868-9a0c-51ce6c91b997" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a57d-c93e-7049-b6ee-20918cdef85f" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_01a1a57d-c93e-7868-9a0c-51ce6c91b997" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_01a1a57d-c93e-792b-95b5-1fbd6f8e482c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1a57d-c93e-7049-b6ee-20918cdef85f" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_01a1a57d-c93e-792b-95b5-1fbd6f8e482c" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofCondensedConsolidatedStatementsofCashFlowsDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofCondensedConsolidatedStatementsofCashFlowsDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofCondensedConsolidatedStatementsofCashFlowsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1afa6-5114-7f6f-a7ff-8666d4e622e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfErrorCorrectionsAndPriorPeriodAdjustmentRestatementTable_01a1afa6-5114-785d-87de-e355654bc6a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfErrorCorrectionsAndPriorPeriodAdjustmentRestatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1afa6-5114-7f6f-a7ff-8666d4e622e8" xlink:to="loc_us-gaap_ScheduleOfErrorCorrectionsAndPriorPeriodAdjustmentRestatementTable_01a1afa6-5114-785d-87de-e355654bc6a8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAxis_01a1afa6-5114-7dc4-8e0e-b6a3af5097f0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfErrorCorrectionsAndPriorPeriodAdjustmentRestatementTable_01a1afa6-5114-785d-87de-e355654bc6a8" xlink:to="loc_srt_RestatementAxis_01a1afa6-5114-7dc4-8e0e-b6a3af5097f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_01a1afa6-5114-7dc4-8e0e-b6a3af5097f0_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RestatementAxis_01a1afa6-5114-7dc4-8e0e-b6a3af5097f0" xlink:to="loc_srt_RestatementDomain_01a1afa6-5114-7dc4-8e0e-b6a3af5097f0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_01a1afa6-5114-7520-a744-35f9629851e9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RestatementAxis_01a1afa6-5114-7dc4-8e0e-b6a3af5097f0" xlink:to="loc_srt_RestatementDomain_01a1afa6-5114-7520-a744-35f9629851e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioPreviouslyReportedMember_01a1afa6-5114-735c-8148-fcd3c4a8bb1d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioPreviouslyReportedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_01a1afa6-5114-7520-a744-35f9629851e9" xlink:to="loc_srt_ScenarioPreviouslyReportedMember_01a1afa6-5114-735c-8148-fcd3c4a8bb1d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAdjustmentMember_01a1afa6-5114-71cb-bbce-fb73405e5df9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_01a1afa6-5114-7520-a744-35f9629851e9" xlink:to="loc_srt_RestatementAdjustmentMember_01a1afa6-5114-71cb-bbce-fb73405e5df9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_01a1afa6-5114-75f4-9d30-e7ea294040f0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1afa6-5114-7f6f-a7ff-8666d4e622e8" xlink:to="loc_us-gaap_ProfitLoss_01a1afa6-5114-75f4-9d30-e7ea294040f0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAmortizationAndAccretionNet_01a1afa6-5114-7a90-91b7-4395f1bec91f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationAmortizationAndAccretionNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1afa6-5114-7f6f-a7ff-8666d4e622e8" xlink:to="loc_us-gaap_DepreciationAmortizationAndAccretionNet_01a1afa6-5114-7a90-91b7-4395f1bec91f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_01a1afa6-5114-76d4-98c9-f943680a0775" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1afa6-5114-7f6f-a7ff-8666d4e622e8" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_01a1afa6-5114-76d4-98c9-f943680a0775" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_01a1afa6-5114-7a83-9a75-b6c481727dee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1afa6-5114-7f6f-a7ff-8666d4e622e8" xlink:to="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_01a1afa6-5114-7a83-9a75-b6c481727dee" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_01a1afa6-5114-7374-8d11-d3cc0c0684cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1afa6-5114-7f6f-a7ff-8666d4e622e8" xlink:to="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_01a1afa6-5114-7374-8d11-d3cc0c0684cb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_01a1afb4-36ba-7691-a7a5-9164b4bf4395" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1afa6-5114-7f6f-a7ff-8666d4e622e8" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_01a1afb4-36ba-7691-a7a5-9164b4bf4395" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_01a1afa6-5114-7b29-ace2-098875629447" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1afa6-5114-7f6f-a7ff-8666d4e622e8" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_01a1afa6-5114-7b29-ace2-098875629447" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromShortTermInvestments_01a1afa6-5114-72e3-864a-c0562f7d388c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForProceedsFromShortTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1afa6-5114-7f6f-a7ff-8666d4e622e8" xlink:to="loc_us-gaap_PaymentsForProceedsFromShortTermInvestments_01a1afa6-5114-72e3-864a-c0562f7d388c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_01a1afa6-5114-738d-9e8c-6363504dd860" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1afa6-5114-7f6f-a7ff-8666d4e622e8" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_01a1afa6-5114-738d-9e8c-6363504dd860" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect_01a1afa6-5114-71cf-8bf8-36a894f34e03" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementLineItems_01a1afa6-5114-7f6f-a7ff-8666d4e622e8" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect_01a1afa6-5114-71cf-8bf8-36a894f34e03" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/INVESTMENTSINOTHERENTITIESANDVARIABLEINTERESTENTITIESNarrativeDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#INVESTMENTSINOTHERENTITIESANDVARIABLEINTERESTENTITIESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/INVESTMENTSINOTHERENTITIESANDVARIABLEINTERESTENTITIESNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-7e84-afb9-4b170f9cec22" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a17520-7eac-7a8f-bd14-ad58b5fd31a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-7e84-afb9-4b170f9cec22" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a17520-7eac-7a8f-bd14-ad58b5fd31a5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_01a17520-7eac-7d74-82d8-219bc2e36bc6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a17520-7eac-7a8f-bd14-ad58b5fd31a5" xlink:to="loc_srt_OwnershipAxis_01a17520-7eac-7d74-82d8-219bc2e36bc6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_01a17520-7eac-7d74-82d8-219bc2e36bc6_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_01a17520-7eac-7d74-82d8-219bc2e36bc6" xlink:to="loc_srt_OwnershipDomain_01a17520-7eac-7d74-82d8-219bc2e36bc6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_01a17520-7eac-7e19-a40b-afc4df549482" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_01a17520-7eac-7d74-82d8-219bc2e36bc6" xlink:to="loc_srt_OwnershipDomain_01a17520-7eac-7e19-a40b-afc4df549482" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RNGFacilityMember_01a17520-7eac-7c38-af6d-d696f699776a" xlink:href="wdq-20260930.xsd#wdq_RNGFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_01a17520-7eac-7e19-a40b-afc4df549482" xlink:to="loc_wdq_RNGFacilityMember_01a17520-7eac-7c38-af6d-d696f699776a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a17520-7eac-7407-8429-501e483544f5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a17520-7eac-7a8f-bd14-ad58b5fd31a5" xlink:to="loc_srt_RangeAxis_01a17520-7eac-7407-8429-501e483544f5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a17520-7eac-7407-8429-501e483544f5_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_01a17520-7eac-7407-8429-501e483544f5" xlink:to="loc_srt_RangeMember_01a17520-7eac-7407-8429-501e483544f5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a17520-7eac-706d-ae96-8d3161f9b46e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_01a17520-7eac-7407-8429-501e483544f5" xlink:to="loc_srt_RangeMember_01a17520-7eac-706d-ae96-8d3161f9b46e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a17520-7eac-7ae9-bad9-4c3bd30f5433" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a17520-7eac-706d-ae96-8d3161f9b46e" xlink:to="loc_srt_MaximumMember_01a17520-7eac-7ae9-bad9-4c3bd30f5433" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_01a17520-7eac-7e63-9a3f-2a991e60a694" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a17520-7eac-706d-ae96-8d3161f9b46e" xlink:to="loc_srt_MinimumMember_01a17520-7eac-7e63-9a3f-2a991e60a694" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a17520-7eac-78bd-9e47-2b45e43601ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a17520-7eac-7a8f-bd14-ad58b5fd31a5" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a17520-7eac-78bd-9e47-2b45e43601ab" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a17520-7eac-78bd-9e47-2b45e43601ab_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a17520-7eac-78bd-9e47-2b45e43601ab" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a17520-7eac-78bd-9e47-2b45e43601ab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a17520-7eac-74d1-8cca-3d1ad121cea7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a17520-7eac-78bd-9e47-2b45e43601ab" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a17520-7eac-74d1-8cca-3d1ad121cea7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetUnderConstructionMember_01a17520-7eac-7703-b383-d0ba30a72782" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetUnderConstructionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a17520-7eac-74d1-8cca-3d1ad121cea7" xlink:to="loc_us-gaap_AssetUnderConstructionMember_01a17520-7eac-7703-b383-d0ba30a72782" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RenewablePowerMeasure_01a17520-7eac-7a50-9c41-0672dbc92809" xlink:href="wdq-20260930.xsd#wdq_RenewablePowerMeasure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-7e84-afb9-4b170f9cec22" xlink:to="loc_wdq_RenewablePowerMeasure_01a17520-7eac-7a50-9c41-0672dbc92809" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquity_01a17520-7eac-7241-8b75-8feb9a51acc7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-7e84-afb9-4b170f9cec22" xlink:to="loc_us-gaap_EquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquity_01a17520-7eac-7241-8b75-8feb9a51acc7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_01a17520-7eac-716e-a941-a907f09a4f0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-7e84-afb9-4b170f9cec22" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_01a17520-7eac-716e-a941-a907f09a4f0b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_EquityMethodInvestmentAmortizationOfBasisDifferential_01a17520-7eac-7611-a789-96d38f97bcf5" xlink:href="wdq-20260930.xsd#wdq_EquityMethodInvestmentAmortizationOfBasisDifferential"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-7e84-afb9-4b170f9cec22" xlink:to="loc_wdq_EquityMethodInvestmentAmortizationOfBasisDifferential_01a17520-7eac-7611-a789-96d38f97bcf5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_EquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquityInvestmentTaxCredit_01a1c115-8df0-7950-8259-bce25b4d61a9" xlink:href="wdq-20260930.xsd#wdq_EquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquityInvestmentTaxCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-7e84-afb9-4b170f9cec22" xlink:to="loc_wdq_EquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquityInvestmentTaxCredit_01a1c115-8df0-7950-8259-bce25b4d61a9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_EquityMethodInvestmentAmortizationOfBasisDifferentialInvestmentTaxCredit_01a1c115-cb75-7bf9-b98c-ccc9d7a537ba" xlink:href="wdq-20260930.xsd#wdq_EquityMethodInvestmentAmortizationOfBasisDifferentialInvestmentTaxCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-7e84-afb9-4b170f9cec22" xlink:to="loc_wdq_EquityMethodInvestmentAmortizationOfBasisDifferentialInvestmentTaxCredit_01a1c115-cb75-7bf9-b98c-ccc9d7a537ba" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/INVESTMENTSINOTHERENTITIESANDVARIABLEINTERESTENTITIESOwnershipInterestsandCarryingValuesofInvestmentinOtherEntitiesDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#INVESTMENTSINOTHERENTITIESANDVARIABLEINTERESTENTITIESOwnershipInterestsandCarryingValuesofInvestmentinOtherEntitiesDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/INVESTMENTSINOTHERENTITIESANDVARIABLEINTERESTENTITIESOwnershipInterestsandCarryingValuesofInvestmentinOtherEntitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-7fe5-a199-f77ea568879a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a17520-7eac-791f-bd8d-de2cb64f1bcc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-7fe5-a199-f77ea568879a" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a17520-7eac-791f-bd8d-de2cb64f1bcc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a17520-7eac-771a-8718-ba81bdfa02b2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a17520-7eac-791f-bd8d-de2cb64f1bcc" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a17520-7eac-771a-8718-ba81bdfa02b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_01a17520-7eac-771a-8718-ba81bdfa02b2_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a17520-7eac-771a-8718-ba81bdfa02b2" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_01a17520-7eac-771a-8718-ba81bdfa02b2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_01a17520-7eac-72e6-bf98-7dbd09936400" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a17520-7eac-771a-8718-ba81bdfa02b2" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_01a17520-7eac-72e6-bf98-7dbd09936400" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_PineBendMember_01a17520-7eac-7f61-b03c-972b3d92543b" xlink:href="wdq-20260930.xsd#wdq_PineBendMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_01a17520-7eac-72e6-bf98-7dbd09936400" xlink:to="loc_wdq_PineBendMember_01a17520-7eac-7f61-b03c-972b3d92543b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_NobleRoadMember_01a17520-7eac-7e98-b789-4c9887ff5e5f" xlink:href="wdq-20260930.xsd#wdq_NobleRoadMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_01a17520-7eac-72e6-bf98-7dbd09936400" xlink:to="loc_wdq_NobleRoadMember_01a17520-7eac-7e98-b789-4c9887ff5e5f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_GREPBTBHoldingsLLCGREPMember_01a17520-7eac-74ce-b2b0-f51a940e0552" xlink:href="wdq-20260930.xsd#wdq_GREPBTBHoldingsLLCGREPMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_01a17520-7eac-72e6-bf98-7dbd09936400" xlink:to="loc_wdq_GREPBTBHoldingsLLCGREPMember_01a17520-7eac-74ce-b2b0-f51a940e0552" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_SJILandfillRNGLLCSJILRNGMember_01a17520-7eac-721b-b6d1-b88786e8857a" xlink:href="wdq-20260930.xsd#wdq_SJILandfillRNGLLCSJILRNGMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_01a17520-7eac-72e6-bf98-7dbd09936400" xlink:to="loc_wdq_SJILandfillRNGLLCSJILRNGMember_01a17520-7eac-721b-b6d1-b88786e8857a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_ParagonMember_01a17520-7eac-76b4-b01e-6ea474d51b15" xlink:href="wdq-20260930.xsd#wdq_ParagonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_01a17520-7eac-72e6-bf98-7dbd09936400" xlink:to="loc_wdq_ParagonMember_01a17520-7eac-76b4-b01e-6ea474d51b15" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_OtherMember_01a17520-7eac-756b-9f01-dfc08b003e43" xlink:href="wdq-20260930.xsd#wdq_OtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_01a17520-7eac-72e6-bf98-7dbd09936400" xlink:to="loc_wdq_OtherMember_01a17520-7eac-756b-9f01-dfc08b003e43" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_01a17520-7eac-714b-9bc0-cb44cd3c9da5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-7fe5-a199-f77ea568879a" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_01a17520-7eac-714b-9bc0-cb44cd3c9da5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_01a17520-7eac-7b44-bec4-289feb216b4c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-7fe5-a199-f77ea568879a" xlink:to="loc_us-gaap_EquityMethodInvestments_01a17520-7eac-7b44-bec4-289feb216b4c" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/INVESTMENTSINOTHERENTITIESANDVARIABLEINTERESTENTITIESLossFromEquityMethodInvestmentsDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#INVESTMENTSINOTHERENTITIESANDVARIABLEINTERESTENTITIESLossFromEquityMethodInvestmentsDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/INVESTMENTSINOTHERENTITIESANDVARIABLEINTERESTENTITIESLossFromEquityMethodInvestmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-71ca-84c8-c150738f2fbb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a17520-7eac-7fbe-a40e-4b10364dc874" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-71ca-84c8-c150738f2fbb" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a17520-7eac-7fbe-a40e-4b10364dc874" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_01a17520-7eac-72ca-9685-ca91c057a0e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a17520-7eac-7fbe-a40e-4b10364dc874" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_01a17520-7eac-72ca-9685-ca91c057a0e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_01a17520-7eac-72ca-9685-ca91c057a0e4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_01a17520-7eac-72ca-9685-ca91c057a0e4" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_01a17520-7eac-72ca-9685-ca91c057a0e4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_01a17520-7eac-7477-9b1b-eb8bcc178026" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_01a17520-7eac-72ca-9685-ca91c057a0e4" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_01a17520-7eac-7477-9b1b-eb8bcc178026" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeOrGroupOfInvesteesMember_01a17520-7eac-70df-a65c-68c2b4e2daed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeOrGroupOfInvesteesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_01a17520-7eac-7477-9b1b-eb8bcc178026" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeOrGroupOfInvesteesMember_01a17520-7eac-70df-a65c-68c2b4e2daed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_01a17520-7eac-7eee-ac9b-2238b5ea112f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-71ca-84c8-c150738f2fbb" xlink:to="loc_us-gaap_Revenues_01a17520-7eac-7eee-ac9b-2238b5ea112f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossProfit_01a17520-7eac-7b5f-81c0-24fd35822a21" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GrossProfit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-71ca-84c8-c150738f2fbb" xlink:to="loc_us-gaap_GrossProfit_01a17520-7eac-7b5f-81c0-24fd35822a21" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_01a17520-7eac-7061-b3c2-1238a19438e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-71ca-84c8-c150738f2fbb" xlink:to="loc_us-gaap_AssetsCurrent_01a17520-7eac-7061-b3c2-1238a19438e8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNoncurrent_01a17520-7eac-72e1-ba99-7328c8fa21bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-71ca-84c8-c150738f2fbb" xlink:to="loc_us-gaap_AssetsNoncurrent_01a17520-7eac-72e1-ba99-7328c8fa21bc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_01a17520-7eac-736c-a56d-d46457117c22" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-71ca-84c8-c150738f2fbb" xlink:to="loc_us-gaap_Assets_01a17520-7eac-736c-a56d-d46457117c22" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_01a17520-7eac-7060-a649-3101ccd717d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-71ca-84c8-c150738f2fbb" xlink:to="loc_us-gaap_LiabilitiesCurrent_01a17520-7eac-7060-a649-3101ccd717d6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesNoncurrent_01a17520-7eac-7ea5-aff2-831f4e2e6af1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-71ca-84c8-c150738f2fbb" xlink:to="loc_us-gaap_LiabilitiesNoncurrent_01a17520-7eac-7ea5-aff2-831f4e2e6af1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_01a17520-7eac-716e-9f5f-b10e01ea91bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a17520-7eac-71ca-84c8-c150738f2fbb" xlink:to="loc_us-gaap_Liabilities_01a17520-7eac-716e-9f5f-b10e01ea91bf" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/LOANSBorrowingsUndertheVariousDebtFacilitiesDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#LOANSBorrowingsUndertheVariousDebtFacilitiesDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/LOANSBorrowingsUndertheVariousDebtFacilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_01a17520-7eac-79ef-8e43-38a1db942eaf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_01a17520-7eac-7527-9289-71150d98717b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a17520-7eac-79ef-8e43-38a1db942eaf" xlink:to="loc_us-gaap_DebtInstrumentTable_01a17520-7eac-7527-9289-71150d98717b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_01a17520-7eac-7dfe-bb34-2f2f5245adfb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a17520-7eac-7527-9289-71150d98717b" xlink:to="loc_us-gaap_DebtInstrumentAxis_01a17520-7eac-7dfe-bb34-2f2f5245adfb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a17520-7eac-7dfe-bb34-2f2f5245adfb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_01a17520-7eac-7dfe-bb34-2f2f5245adfb" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a17520-7eac-7dfe-bb34-2f2f5245adfb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a17520-7eac-7635-aaa0-e2d21473e9c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_01a17520-7eac-7dfe-bb34-2f2f5245adfb" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a17520-7eac-7635-aaa0-e2d21473e9c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_OpalTermLoanMember_01a17520-7eac-78c7-a889-9249ef7aed05" xlink:href="wdq-20260930.xsd#wdq_OpalTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a17520-7eac-7635-aaa0-e2d21473e9c0" xlink:to="loc_wdq_OpalTermLoanMember_01a17520-7eac-78c7-a889-9249ef7aed05" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RevolvingLoanMember_01a17520-7eac-7f6e-8b81-ace6eacffbe7" xlink:href="wdq-20260930.xsd#wdq_RevolvingLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a17520-7eac-7635-aaa0-e2d21473e9c0" xlink:to="loc_wdq_RevolvingLoanMember_01a17520-7eac-7f6e-8b81-ace6eacffbe7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_SunomaLoanMember_01a17520-7eac-7ac7-a094-f67ad456606d" xlink:href="wdq-20260930.xsd#wdq_SunomaLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a17520-7eac-7635-aaa0-e2d21473e9c0" xlink:to="loc_wdq_SunomaLoanMember_01a17520-7eac-7ac7-a094-f67ad456606d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_EquipmentLoanMember_01a17520-7eac-71a0-a81f-6d4f4191e21c" xlink:href="wdq-20260930.xsd#wdq_EquipmentLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a17520-7eac-7635-aaa0-e2d21473e9c0" xlink:to="loc_wdq_EquipmentLoanMember_01a17520-7eac-71a0-a81f-6d4f4191e21c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_01a17520-7eac-7f3b-b7fc-dab6e3c08b95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a17520-7eac-7527-9289-71150d98717b" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_01a17520-7eac-7f3b-b7fc-dab6e3c08b95" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a17520-7eac-7f3b-b7fc-dab6e3c08b95_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a17520-7eac-7f3b-b7fc-dab6e3c08b95" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a17520-7eac-7f3b-b7fc-dab6e3c08b95_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a17520-7eac-7d73-bcec-4d46f206b0b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a17520-7eac-7f3b-b7fc-dab6e3c08b95" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a17520-7eac-7d73-bcec-4d46f206b0b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_01a17520-7eac-716f-8967-16e67d8ee9b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a17520-7eac-7d73-bcec-4d46f206b0b2" xlink:to="loc_us-gaap_SecuredDebtMember_01a17520-7eac-716f-8967-16e67d8ee9b6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_01a17520-7eac-7edd-88f0-64e97bd697b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a17520-7eac-79ef-8e43-38a1db942eaf" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_01a17520-7eac-7edd-88f0-64e97bd697b7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_01a17520-7eac-7fde-917f-38ade09c7500" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a17520-7eac-79ef-8e43-38a1db942eaf" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_01a17520-7eac-7fde-917f-38ade09c7500" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_01a17520-7eac-718b-b0bc-7a3261b7638e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a17520-7eac-79ef-8e43-38a1db942eaf" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_01a17520-7eac-718b-b0bc-7a3261b7638e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_01a17520-7eac-75bd-944c-68ee540e9640" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a17520-7eac-79ef-8e43-38a1db942eaf" xlink:to="loc_us-gaap_LongTermDebtCurrent_01a17520-7eac-75bd-944c-68ee540e9640" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_01a17520-7eac-712f-a2aa-1b7867ae8ab3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a17520-7eac-79ef-8e43-38a1db942eaf" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_01a17520-7eac-712f-a2aa-1b7867ae8ab3" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/LOANSOpalTermLoanNarrativeDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#LOANSOpalTermLoanNarrativeDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/LOANSOpalTermLoanNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_01a17520-7eac-78b4-80ff-213c00b1f35f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_01a17520-7eac-7bf0-b211-7754caa6789a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a17520-7eac-78b4-80ff-213c00b1f35f" xlink:to="loc_us-gaap_DebtInstrumentTable_01a17520-7eac-7bf0-b211-7754caa6789a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_01a17520-7eac-7308-ae77-33f7bbcc977a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a17520-7eac-7bf0-b211-7754caa6789a" xlink:to="loc_us-gaap_CreditFacilityAxis_01a17520-7eac-7308-ae77-33f7bbcc977a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a17520-7eac-7308-ae77-33f7bbcc977a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_01a17520-7eac-7308-ae77-33f7bbcc977a" xlink:to="loc_us-gaap_CreditFacilityDomain_01a17520-7eac-7308-ae77-33f7bbcc977a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a17520-7eac-7140-9586-b844c00324f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_01a17520-7eac-7308-ae77-33f7bbcc977a" xlink:to="loc_us-gaap_CreditFacilityDomain_01a17520-7eac-7140-9586-b844c00324f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_01a17520-7eac-7482-8d7e-7780d761fb6c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_01a17520-7eac-7140-9586-b844c00324f2" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_01a17520-7eac-7482-8d7e-7780d761fb6c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_01a17520-7eac-7e21-be69-b0ab8c53ad59" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a17520-7eac-7bf0-b211-7754caa6789a" xlink:to="loc_us-gaap_DebtInstrumentAxis_01a17520-7eac-7e21-be69-b0ab8c53ad59" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a17520-7eac-7e21-be69-b0ab8c53ad59_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_01a17520-7eac-7e21-be69-b0ab8c53ad59" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a17520-7eac-7e21-be69-b0ab8c53ad59_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a17520-7eac-759b-ac93-4ef64273cf30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_01a17520-7eac-7e21-be69-b0ab8c53ad59" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a17520-7eac-759b-ac93-4ef64273cf30" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_OpalTermLoanMember_01a17520-7eac-75bb-876a-141189fbb540" xlink:href="wdq-20260930.xsd#wdq_OpalTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a17520-7eac-759b-ac93-4ef64273cf30" xlink:to="loc_wdq_OpalTermLoanMember_01a17520-7eac-75bb-876a-141189fbb540" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_CreditAgreementMember_01a17520-7eac-794f-8804-1357ae65c43e" xlink:href="wdq-20260930.xsd#wdq_CreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a17520-7eac-759b-ac93-4ef64273cf30" xlink:to="loc_wdq_CreditAgreementMember_01a17520-7eac-794f-8804-1357ae65c43e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_01a17520-7eac-7890-8c88-09b49dc52da7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a17520-7eac-7bf0-b211-7754caa6789a" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_01a17520-7eac-7890-8c88-09b49dc52da7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a17520-7eac-7890-8c88-09b49dc52da7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a17520-7eac-7890-8c88-09b49dc52da7" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a17520-7eac-7890-8c88-09b49dc52da7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a17520-7eac-7621-ba85-5048af82e509" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a17520-7eac-7890-8c88-09b49dc52da7" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a17520-7eac-7621-ba85-5048af82e509" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_01a17520-7eac-7eb7-954d-b37fa48405a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a17520-7eac-7621-ba85-5048af82e509" xlink:to="loc_us-gaap_LineOfCreditMember_01a17520-7eac-7eb7-954d-b37fa48405a8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_01a17520-7eac-7015-b15e-aa3c42ece2c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a17520-7eac-7bf0-b211-7754caa6789a" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_01a17520-7eac-7015-b15e-aa3c42ece2c4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_01a17520-7eac-7015-b15e-aa3c42ece2c4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_01a17520-7eac-7015-b15e-aa3c42ece2c4" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_01a17520-7eac-7015-b15e-aa3c42ece2c4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_01a17520-7eac-77b3-bba8-8623377157d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_01a17520-7eac-7015-b15e-aa3c42ece2c4" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_01a17520-7eac-77b3-bba8-8623377157d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_ContributionToMaintainCovenantComplianceMember_01a17520-7eac-7053-94c5-1f81b6b21290" xlink:href="wdq-20260930.xsd#wdq_ContributionToMaintainCovenantComplianceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_01a17520-7eac-77b3-bba8-8623377157d5" xlink:to="loc_wdq_ContributionToMaintainCovenantComplianceMember_01a17520-7eac-7053-94c5-1f81b6b21290" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7eac-7863-97a2-4a3972428d4c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a17520-7eac-7bf0-b211-7754caa6789a" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7eac-7863-97a2-4a3972428d4c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a17520-7eac-7863-97a2-4a3972428d4c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7eac-7863-97a2-4a3972428d4c" xlink:to="loc_us-gaap_RelatedPartyDomain_01a17520-7eac-7863-97a2-4a3972428d4c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a17520-7eac-7497-b46e-34aceb34dea0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7eac-7863-97a2-4a3972428d4c" xlink:to="loc_us-gaap_RelatedPartyDomain_01a17520-7eac-7497-b46e-34aceb34dea0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_HoldCoMember_01a17520-7eac-7c0b-b157-435935864dca" xlink:href="wdq-20260930.xsd#wdq_HoldCoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a17520-7eac-7497-b46e-34aceb34dea0" xlink:to="loc_wdq_HoldCoMember_01a17520-7eac-7c0b-b157-435935864dca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLongTermLinesOfCredit_01a17520-7eac-7c9b-8ea1-ce615ed7e253" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromLongTermLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a17520-7eac-78b4-80ff-213c00b1f35f" xlink:to="loc_us-gaap_ProceedsFromLongTermLinesOfCredit_01a17520-7eac-7c9b-8ea1-ce615ed7e253" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLongTermLinesOfCredit_01a17520-7eac-7a7a-b7b6-49df80e1876d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfLongTermLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a17520-7eac-78b4-80ff-213c00b1f35f" xlink:to="loc_us-gaap_RepaymentsOfLongTermLinesOfCredit_01a17520-7eac-7a7a-b7b6-49df80e1876d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt_01a17520-7eac-702c-b8e4-c7f48191d84a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a17520-7eac-78b4-80ff-213c00b1f35f" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt_01a17520-7eac-702c-b8e4-c7f48191d84a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_DebtInstrumentThresholdTradingDaysOfCashSweep_01a17520-7eac-7785-a362-51345dd4960b" xlink:href="wdq-20260930.xsd#wdq_DebtInstrumentThresholdTradingDaysOfCashSweep"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a17520-7eac-78b4-80ff-213c00b1f35f" xlink:to="loc_wdq_DebtInstrumentThresholdTradingDaysOfCashSweep_01a17520-7eac-7785-a362-51345dd4960b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_DebtInstrumentThresholdPercentageOfCashSweep_01a17520-7eac-7bc8-8280-9694e7928e3b" xlink:href="wdq-20260930.xsd#wdq_DebtInstrumentThresholdPercentageOfCashSweep"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a17520-7eac-78b4-80ff-213c00b1f35f" xlink:to="loc_wdq_DebtInstrumentThresholdPercentageOfCashSweep_01a17520-7eac-7bc8-8280-9694e7928e3b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_01a17520-7eac-74fc-9833-b8c080ff3085" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionAmountsOfTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a17520-7eac-78b4-80ff-213c00b1f35f" xlink:to="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_01a17520-7eac-74fc-9833-b8c080ff3085" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/LOANSSunomaLoanNarrativeDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#LOANSSunomaLoanNarrativeDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/LOANSSunomaLoanNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_01a17520-7eac-75b1-80e8-baa7d9c3b0c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_01a17520-7eac-7fb0-864f-3f5eb2234ee7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a17520-7eac-75b1-80e8-baa7d9c3b0c8" xlink:to="loc_us-gaap_DebtInstrumentTable_01a17520-7eac-7fb0-864f-3f5eb2234ee7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_01a17520-7eac-7f35-9232-9f61a6212268" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a17520-7eac-7fb0-864f-3f5eb2234ee7" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_01a17520-7eac-7f35-9232-9f61a6212268" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a17520-7eac-7f35-9232-9f61a6212268_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a17520-7eac-7f35-9232-9f61a6212268" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a17520-7eac-7f35-9232-9f61a6212268_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a17520-7eac-7bf0-8db3-bcebee08291d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a17520-7eac-7f35-9232-9f61a6212268" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a17520-7eac-7bf0-8db3-bcebee08291d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_01a17520-7eac-7227-82c8-c3d48fb3df11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a17520-7eac-7bf0-8db3-bcebee08291d" xlink:to="loc_us-gaap_LetterOfCreditMember_01a17520-7eac-7227-82c8-c3d48fb3df11" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLongTermLinesOfCredit_01a17520-7eac-70cc-82f6-c1cde235e71c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromLongTermLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a17520-7eac-75b1-80e8-baa7d9c3b0c8" xlink:to="loc_us-gaap_ProceedsFromLongTermLinesOfCredit_01a17520-7eac-70cc-82f6-c1cde235e71c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/LEASESNarrativeDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#LEASESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/LEASESNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorLeaseDescriptionLineItems_01a17520-7ead-730f-b0ae-af735f015e04" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorLeaseDescriptionTable_01a17520-7ead-7acc-82e9-0e24fe9a484a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LessorLeaseDescriptionLineItems_01a17520-7ead-730f-b0ae-af735f015e04" xlink:to="loc_us-gaap_LessorLeaseDescriptionTable_01a17520-7ead-7acc-82e9-0e24fe9a484a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_01a17520-7ead-792a-a078-e9d6ab9e00bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LessorLeaseDescriptionTable_01a17520-7ead-7acc-82e9-0e24fe9a484a" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_01a17520-7ead-792a-a078-e9d6ab9e00bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesTypeLeaseRevenue_01a17520-7ead-7f70-86ab-41461229b6bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SalesTypeLeaseRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LessorLeaseDescriptionLineItems_01a17520-7ead-730f-b0ae-af735f015e04" xlink:to="loc_us-gaap_SalesTypeLeaseRevenue_01a17520-7ead-7f70-86ab-41461229b6bc" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/LEASESNarrativeDetails_1" xlink:type="simple" xlink:href="wdq-20260930.xsd#LEASESNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/LEASESNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorLeaseDescriptionLineItems_01a17520-7ead-730f-b0ae-af735f015e04" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorLeaseDescriptionTable_01a17520-7ead-7acc-82e9-0e24fe9a484a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LessorLeaseDescriptionLineItems_01a17520-7ead-730f-b0ae-af735f015e04" xlink:to="loc_us-gaap_LessorLeaseDescriptionTable_01a17520-7ead-7acc-82e9-0e24fe9a484a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesTypeLeaseRevenue_01a17520-7ead-7f70-86ab-41461229b6bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SalesTypeLeaseRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LessorLeaseDescriptionLineItems_01a17520-7ead-730f-b0ae-af735f015e04" xlink:to="loc_us-gaap_SalesTypeLeaseRevenue_01a17520-7ead-7f70-86ab-41461229b6bc" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/DERIVATIVEFINANCIALINSTRUMENTSANDFAIRVALUEMEASUREMENTSNarrativeDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#DERIVATIVEFINANCIALINSTRUMENTSANDFAIRVALUEMEASUREMENTSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/DERIVATIVEFINANCIALINSTRUMENTSANDFAIRVALUEMEASUREMENTSNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_01a17520-7ead-7c1c-a49c-2b40f82f4069" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_01a17520-7ead-7ac3-a5fc-fce34f9c901b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7ead-7c1c-a49c-2b40f82f4069" xlink:to="loc_us-gaap_DerivativeTable_01a17520-7ead-7ac3-a5fc-fce34f9c901b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7ead-7618-88ad-144fb2dd9d30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a17520-7ead-7ac3-a5fc-fce34f9c901b" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7ead-7618-88ad-144fb2dd9d30" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-7618-88ad-144fb2dd9d30_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7ead-7618-88ad-144fb2dd9d30" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-7618-88ad-144fb2dd9d30_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-7caf-9ba5-eb01295e8f09" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7ead-7618-88ad-144fb2dd9d30" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-7caf-9ba5-eb01295e8f09" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_01a17520-7ead-7d05-9aae-39787664a2f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-7caf-9ba5-eb01295e8f09" xlink:to="loc_us-gaap_InterestRateSwapMember_01a17520-7ead-7d05-9aae-39787664a2f2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_01a17520-7ead-7abc-8d40-739051fde3bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a17520-7ead-7ac3-a5fc-fce34f9c901b" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_01a17520-7ead-7abc-8d40-739051fde3bc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_01a17520-7ead-7abc-8d40-739051fde3bc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_01a17520-7ead-7abc-8d40-739051fde3bc" xlink:to="loc_us-gaap_HedgingRelationshipDomain_01a17520-7ead-7abc-8d40-739051fde3bc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_01a17520-7ead-74f3-86da-d0000f9286f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_01a17520-7ead-7abc-8d40-739051fde3bc" xlink:to="loc_us-gaap_HedgingRelationshipDomain_01a17520-7ead-74f3-86da-d0000f9286f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_01a17520-7ead-76b7-ac02-80ce4d9c0aa4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_01a17520-7ead-74f3-86da-d0000f9286f4" xlink:to="loc_us-gaap_CashFlowHedgingMember_01a17520-7ead-76b7-ac02-80ce4d9c0aa4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetsCurrent_01a17520-7ead-7919-b7b9-f7a0dc872c4f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7ead-7c1c-a49c-2b40f82f4069" xlink:to="loc_us-gaap_DerivativeAssetsCurrent_01a17520-7ead-7919-b7b9-f7a0dc872c4f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_WarrantsIssued_01a17520-7ead-717b-ad8e-1fe27281c987" xlink:href="wdq-20260930.xsd#wdq_WarrantsIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7ead-7c1c-a49c-2b40f82f4069" xlink:to="loc_wdq_WarrantsIssued_01a17520-7ead-717b-ad8e-1fe27281c987" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAdjustmentOfWarrants_01a17520-7ead-77c5-a2bf-8e6d3f008d63" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAdjustmentOfWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7ead-7c1c-a49c-2b40f82f4069" xlink:to="loc_us-gaap_FairValueAdjustmentOfWarrants_01a17520-7ead-77c5-a2bf-8e6d3f008d63" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstanding_01a17520-7ead-7eef-a462-3f2bc893f766" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7ead-7c1c-a49c-2b40f82f4069" xlink:to="loc_us-gaap_WarrantsAndRightsOutstanding_01a17520-7ead-7eef-a462-3f2bc893f766" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/DERIVATIVEFINANCIALINSTRUMENTSANDFAIRVALUEMEASUREMENTSInterestRateSwapsDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#DERIVATIVEFINANCIALINSTRUMENTSANDFAIRVALUEMEASUREMENTSInterestRateSwapsDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/DERIVATIVEFINANCIALINSTRUMENTSANDFAIRVALUEMEASUREMENTSInterestRateSwapsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_01a17520-7ead-72cb-9d4c-5c412213cdbb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_01a17520-7ead-7bd4-9811-c219b0f93799" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7ead-72cb-9d4c-5c412213cdbb" xlink:to="loc_us-gaap_DerivativeTable_01a17520-7ead-7bd4-9811-c219b0f93799" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7ead-7b43-a465-87f981e4abd6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a17520-7ead-7bd4-9811-c219b0f93799" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7ead-7b43-a465-87f981e4abd6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-7b43-a465-87f981e4abd6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7ead-7b43-a465-87f981e4abd6" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-7b43-a465-87f981e4abd6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-777f-b416-b8f3fd9aaff1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7ead-7b43-a465-87f981e4abd6" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-777f-b416-b8f3fd9aaff1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_01a17520-7ead-7e2d-80a9-0f03d0cffbcf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-777f-b416-b8f3fd9aaff1" xlink:to="loc_us-gaap_InterestRateSwapMember_01a17520-7ead-7e2d-80a9-0f03d0cffbcf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_01a17520-7ead-7194-9c0c-c5be00fb773d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a17520-7ead-7bd4-9811-c219b0f93799" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_01a17520-7ead-7194-9c0c-c5be00fb773d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_01a17520-7ead-7194-9c0c-c5be00fb773d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_01a17520-7ead-7194-9c0c-c5be00fb773d" xlink:to="loc_us-gaap_HedgingRelationshipDomain_01a17520-7ead-7194-9c0c-c5be00fb773d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_01a17520-7ead-7145-8ccc-b8636633ccec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_01a17520-7ead-7194-9c0c-c5be00fb773d" xlink:to="loc_us-gaap_HedgingRelationshipDomain_01a17520-7ead-7145-8ccc-b8636633ccec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_01a17520-7ead-7c33-91f8-264e9ad55c12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_01a17520-7ead-7145-8ccc-b8636633ccec" xlink:to="loc_us-gaap_CashFlowHedgingMember_01a17520-7ead-7c33-91f8-264e9ad55c12" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetsCurrent_01a17520-7ead-7e80-9a99-ab96032c1b54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7ead-72cb-9d4c-5c412213cdbb" xlink:to="loc_us-gaap_DerivativeAssetsCurrent_01a17520-7ead-7e80-9a99-ab96032c1b54" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetsNoncurrent_01a17520-7ead-77ce-8564-f83289d58d5e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7ead-72cb-9d4c-5c412213cdbb" xlink:to="loc_us-gaap_DerivativeAssetsNoncurrent_01a17520-7ead-77ce-8564-f83289d58d5e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilitiesNoncurrent_01a17520-7ead-702d-82f7-03a2710239f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7ead-72cb-9d4c-5c412213cdbb" xlink:to="loc_us-gaap_DerivativeLiabilitiesNoncurrent_01a17520-7ead-702d-82f7-03a2710239f5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet_01a17520-7ead-7708-8050-956f9ef2b729" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a17520-7ead-72cb-9d4c-5c412213cdbb" xlink:to="loc_us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet_01a17520-7ead-7708-8050-956f9ef2b729" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/DERIVATIVEFINANCIALINSTRUMENTSANDFAIRVALUEMEASUREMENTSEffectofDerivativeInstrumentsonStatementofOperationsDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#DERIVATIVEFINANCIALINSTRUMENTSANDFAIRVALUEMEASUREMENTSEffectofDerivativeInstrumentsonStatementofOperationsDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/DERIVATIVEFINANCIALINSTRUMENTSANDFAIRVALUEMEASUREMENTSEffectofDerivativeInstrumentsonStatementofOperationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01a17520-7ead-7520-ae38-01949b0ca890" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01a17520-7ead-7e96-bddc-d92f531c7ebf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01a17520-7ead-7520-ae38-01949b0ca890" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01a17520-7ead-7e96-bddc-d92f531c7ebf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_01a17520-7ead-7a58-be0d-87b172f225fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01a17520-7ead-7e96-bddc-d92f531c7ebf" xlink:to="loc_us-gaap_HedgingDesignationAxis_01a17520-7ead-7a58-be0d-87b172f225fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_01a17520-7ead-7a58-be0d-87b172f225fc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_01a17520-7ead-7a58-be0d-87b172f225fc" xlink:to="loc_us-gaap_HedgingDesignationDomain_01a17520-7ead-7a58-be0d-87b172f225fc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_01a17520-7ead-770d-8e57-0ba6d1336bd3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_01a17520-7ead-7a58-be0d-87b172f225fc" xlink:to="loc_us-gaap_HedgingDesignationDomain_01a17520-7ead-770d-8e57-0ba6d1336bd3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotDesignatedAsHedgingInstrumentEconomicHedgeMember_01a17520-7ead-7d6f-9bbc-5eb76056e977" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotDesignatedAsHedgingInstrumentEconomicHedgeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_01a17520-7ead-770d-8e57-0ba6d1336bd3" xlink:to="loc_us-gaap_NotDesignatedAsHedgingInstrumentEconomicHedgeMember_01a17520-7ead-7d6f-9bbc-5eb76056e977" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_01a17520-7ead-7a45-96dc-8793e4b57d9b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01a17520-7ead-7e96-bddc-d92f531c7ebf" xlink:to="loc_srt_ProductOrServiceAxis_01a17520-7ead-7a45-96dc-8793e4b57d9b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a17520-7ead-7a45-96dc-8793e4b57d9b_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_01a17520-7ead-7a45-96dc-8793e4b57d9b" xlink:to="loc_srt_ProductsAndServicesDomain_01a17520-7ead-7a45-96dc-8793e4b57d9b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a17520-7ead-72fc-91da-3ae1cfbda51a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_01a17520-7ead-7a45-96dc-8793e4b57d9b" xlink:to="loc_srt_ProductsAndServicesDomain_01a17520-7ead-72fc-91da-3ae1cfbda51a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RNGFuelMember_01a17520-7ead-7c7a-81a0-b9cb5c087f0f" xlink:href="wdq-20260930.xsd#wdq_RNGFuelMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a17520-7ead-72fc-91da-3ae1cfbda51a" xlink:to="loc_wdq_RNGFuelMember_01a17520-7ead-7c7a-81a0-b9cb5c087f0f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7ead-7f2e-bc45-600f76c33da3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01a17520-7ead-7e96-bddc-d92f531c7ebf" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7ead-7f2e-bc45-600f76c33da3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-7f2e-bc45-600f76c33da3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7ead-7f2e-bc45-600f76c33da3" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-7f2e-bc45-600f76c33da3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-7a2c-9e42-7952b6a62cce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7ead-7f2e-bc45-600f76c33da3" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-7a2c-9e42-7952b6a62cce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommodityContractMember_01a17520-7ead-7851-80d2-93a9f33bc86c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommodityContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-7a2c-9e42-7952b6a62cce" xlink:to="loc_us-gaap_CommodityContractMember_01a17520-7ead-7851-80d2-93a9f33bc86c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfCommodityContracts_01a17520-7ead-76bf-b093-c98fda7026e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnSaleOfCommodityContracts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01a17520-7ead-7520-ae38-01949b0ca890" xlink:to="loc_us-gaap_GainLossOnSaleOfCommodityContracts_01a17520-7ead-76bf-b093-c98fda7026e3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrealizedGainLossOnCommodityContracts_01a17520-7ead-7029-a097-45120d09e53f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnrealizedGainLossOnCommodityContracts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01a17520-7ead-7520-ae38-01949b0ca890" xlink:to="loc_us-gaap_UnrealizedGainLossOnCommodityContracts_01a17520-7ead-7029-a097-45120d09e53f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_01a17520-7ead-7365-84b0-d8cb3af31044" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01a17520-7ead-7520-ae38-01949b0ca890" xlink:to="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_01a17520-7ead-7365-84b0-d8cb3af31044" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_01a17520-7ead-71ee-96ce-4daa3222bd66" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01a17520-7ead-7520-ae38-01949b0ca890" xlink:to="loc_us-gaap_DerivativeAssets_01a17520-7ead-71ee-96ce-4daa3222bd66" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/DERIVATIVEFINANCIALINSTRUMENTSANDFAIRVALUEMEASUREMENTSDerivativesFairValuesonBalanceSheetDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#DERIVATIVEFINANCIALINSTRUMENTSANDFAIRVALUEMEASUREMENTSDerivativesFairValuesonBalanceSheetDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/DERIVATIVEFINANCIALINSTRUMENTSANDFAIRVALUEMEASUREMENTSDerivativesFairValuesonBalanceSheetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01a17520-7ead-7e08-a3c3-02d686298560" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01a17520-7ead-7e3a-82a1-c0d67ef96dad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01a17520-7ead-7e08-a3c3-02d686298560" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01a17520-7ead-7e3a-82a1-c0d67ef96dad" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7ead-743e-b5ce-01b95d7dedea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01a17520-7ead-7e3a-82a1-c0d67ef96dad" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7ead-743e-b5ce-01b95d7dedea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-743e-b5ce-01b95d7dedea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7ead-743e-b5ce-01b95d7dedea" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-743e-b5ce-01b95d7dedea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-7df2-b545-b2f2ecc40752" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7ead-743e-b5ce-01b95d7dedea" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-7df2-b545-b2f2ecc40752" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommodityContractMember_01a17520-7ead-769a-bf38-10fef0ab2499" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommodityContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7ead-7df2-b545-b2f2ecc40752" xlink:to="loc_us-gaap_CommodityContractMember_01a17520-7ead-769a-bf38-10fef0ab2499" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_01a17520-7ead-714a-a4ac-3d68df6974dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01a17520-7ead-7e3a-82a1-c0d67ef96dad" xlink:to="loc_us-gaap_HedgingDesignationAxis_01a17520-7ead-714a-a4ac-3d68df6974dc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_01a17520-7ead-714a-a4ac-3d68df6974dc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_01a17520-7ead-714a-a4ac-3d68df6974dc" xlink:to="loc_us-gaap_HedgingDesignationDomain_01a17520-7ead-714a-a4ac-3d68df6974dc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_01a17520-7ead-7cf8-811d-0b4104f15f9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_01a17520-7ead-714a-a4ac-3d68df6974dc" xlink:to="loc_us-gaap_HedgingDesignationDomain_01a17520-7ead-7cf8-811d-0b4104f15f9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotDesignatedAsHedgingInstrumentEconomicHedgeMember_01a17520-7ead-7c7b-9486-6b315ffda1c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotDesignatedAsHedgingInstrumentEconomicHedgeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_01a17520-7ead-7cf8-811d-0b4104f15f9f" xlink:to="loc_us-gaap_NotDesignatedAsHedgingInstrumentEconomicHedgeMember_01a17520-7ead-7c7b-9486-6b315ffda1c5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetsCurrent_01a17520-7ead-7301-850b-ebdc00c88037" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01a17520-7ead-7e08-a3c3-02d686298560" xlink:to="loc_us-gaap_DerivativeAssetsCurrent_01a17520-7ead-7301-850b-ebdc00c88037" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilitiesCurrent_01a17520-7ead-7c23-9f0a-ea1c338fba72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01a17520-7ead-7e08-a3c3-02d686298560" xlink:to="loc_us-gaap_DerivativeLiabilitiesCurrent_01a17520-7ead-7c23-9f0a-ea1c338fba72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetsNoncurrent_01a17520-7ead-7b4b-b2f3-c0daad5fcfae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01a17520-7ead-7e08-a3c3-02d686298560" xlink:to="loc_us-gaap_DerivativeAssetsNoncurrent_01a17520-7ead-7b4b-b2f3-c0daad5fcfae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_01a17520-7ead-7b60-9a99-71bf7df193dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01a17520-7ead-7e08-a3c3-02d686298560" xlink:to="loc_us-gaap_DerivativeAssets_01a17520-7ead-7b60-9a99-71bf7df193dc" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/DERIVATIVEFINANCIALINSTRUMENTSANDFAIRVALUEMEASUREMENTSFairValueMeasurementInputsandValuationTechniquesDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#DERIVATIVEFINANCIALINSTRUMENTSANDFAIRVALUEMEASUREMENTSFairValueMeasurementInputsandValuationTechniquesDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/DERIVATIVEFINANCIALINSTRUMENTSANDFAIRVALUEMEASUREMENTSFairValueMeasurementInputsandValuationTechniquesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01a17520-7f6a-7733-a1b7-91b8fc323112" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01a17520-7ead-761e-8390-382b5b8b16e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01a17520-7f6a-7733-a1b7-91b8fc323112" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01a17520-7ead-761e-8390-382b5b8b16e5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_01a17520-7ead-70c1-a811-9f6fe974cf81" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01a17520-7ead-761e-8390-382b5b8b16e5" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_01a17520-7ead-70c1-a811-9f6fe974cf81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_01a17520-7ead-70c1-a811-9f6fe974cf81_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_01a17520-7ead-70c1-a811-9f6fe974cf81" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_01a17520-7ead-70c1-a811-9f6fe974cf81_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_01a17520-7ead-741f-95d4-e31b38235c85" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_01a17520-7ead-70c1-a811-9f6fe974cf81" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_01a17520-7ead-741f-95d4-e31b38235c85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_01a17520-7ead-7b81-80e5-54a0c479762e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputRiskFreeInterestRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_01a17520-7ead-741f-95d4-e31b38235c85" xlink:to="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_01a17520-7ead-7b81-80e5-54a0c479762e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedTermMember_01a17520-7f6a-7977-9d69-2f9957df6444" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputExpectedTermMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_01a17520-7ead-741f-95d4-e31b38235c85" xlink:to="loc_us-gaap_MeasurementInputExpectedTermMember_01a17520-7f6a-7977-9d69-2f9957df6444" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputPriceVolatilityMember_01a17520-7f6a-72e8-8e0e-0c8804a51bab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputPriceVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_01a17520-7ead-741f-95d4-e31b38235c85" xlink:to="loc_us-gaap_MeasurementInputPriceVolatilityMember_01a17520-7f6a-72e8-8e0e-0c8804a51bab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExercisePriceMember_01a17520-7f6a-7bec-ba8d-79ffc881e231" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputExercisePriceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_01a17520-7ead-741f-95d4-e31b38235c85" xlink:to="loc_us-gaap_MeasurementInputExercisePriceMember_01a17520-7f6a-7bec-ba8d-79ffc881e231" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputSharePriceMember_01a17520-7f6a-741e-829c-baadbd97bc4b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputSharePriceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_01a17520-7ead-741f-95d4-e31b38235c85" xlink:to="loc_us-gaap_MeasurementInputSharePriceMember_01a17520-7f6a-741e-829c-baadbd97bc4b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_01a17520-7f6a-7271-bc02-f02c269839bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstandingMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01a17520-7f6a-7733-a1b7-91b8fc323112" xlink:to="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_01a17520-7f6a-7271-bc02-f02c269839bb" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/DERIVATIVEFINANCIALINSTRUMENTSANDFAIRVALUEMEASUREMENTSAssetsandLiabilitiesMeasuredatFairValueonRecurringBasisDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#DERIVATIVEFINANCIALINSTRUMENTSANDFAIRVALUEMEASUREMENTSAssetsandLiabilitiesMeasuredatFairValueonRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/DERIVATIVEFINANCIALINSTRUMENTSANDFAIRVALUEMEASUREMENTSAssetsandLiabilitiesMeasuredatFairValueonRecurringBasisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a17520-7f6a-7934-99dc-e2fdb89c95cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a17520-7f6a-70c2-acea-cbbecbd72091" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a17520-7f6a-7934-99dc-e2fdb89c95cf" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a17520-7f6a-70c2-acea-cbbecbd72091" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a17520-7f6a-74d6-936b-463edc6fbc31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a17520-7f6a-70c2-acea-cbbecbd72091" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a17520-7f6a-74d6-936b-463edc6fbc31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a17520-7f6a-74d6-936b-463edc6fbc31_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a17520-7f6a-74d6-936b-463edc6fbc31" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a17520-7f6a-74d6-936b-463edc6fbc31_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a17520-7f6a-7571-b61e-512aa0eff8b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a17520-7f6a-74d6-936b-463edc6fbc31" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a17520-7f6a-7571-b61e-512aa0eff8b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_01a17520-7f6a-7460-85f4-9a43440eb63e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a17520-7f6a-7571-b61e-512aa0eff8b8" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_01a17520-7f6a-7460-85f4-9a43440eb63e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_01a17520-7f6a-727d-8304-36dd016fe43d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a17520-7f6a-7571-b61e-512aa0eff8b8" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_01a17520-7f6a-727d-8304-36dd016fe43d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_01a17520-7f6a-7677-9589-9f6ad6b44921" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a17520-7f6a-7571-b61e-512aa0eff8b8" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_01a17520-7f6a-7677-9589-9f6ad6b44921" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_01a17520-7f6a-7cd9-8ba0-81c31fb2fc61" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a17520-7f6a-70c2-acea-cbbecbd72091" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_01a17520-7f6a-7cd9-8ba0-81c31fb2fc61" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_01a17520-7f6a-7cd9-8ba0-81c31fb2fc61_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_01a17520-7f6a-7cd9-8ba0-81c31fb2fc61" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_01a17520-7f6a-7cd9-8ba0-81c31fb2fc61_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_01a17520-7f6a-7a97-b2f6-8818c5d1e3bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_01a17520-7f6a-7cd9-8ba0-81c31fb2fc61" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_01a17520-7f6a-7a97-b2f6-8818c5d1e3bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_01a17520-7f6a-7177-8553-b38d7901e428" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_01a17520-7f6a-7a97-b2f6-8818c5d1e3bc" xlink:to="loc_us-gaap_MoneyMarketFundsMember_01a17520-7f6a-7177-8553-b38d7901e428" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7f6a-7503-89a4-b1bc8ab8e0fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a17520-7f6a-70c2-acea-cbbecbd72091" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7f6a-7503-89a4-b1bc8ab8e0fe" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7f6a-7503-89a4-b1bc8ab8e0fe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7f6a-7503-89a4-b1bc8ab8e0fe" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7f6a-7503-89a4-b1bc8ab8e0fe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7f6a-7407-b59c-248bf82bde84" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7f6a-7503-89a4-b1bc8ab8e0fe" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7f6a-7407-b59c-248bf82bde84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_01a17520-7f6a-76b2-8754-96ae44476d0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7f6a-7407-b59c-248bf82bde84" xlink:to="loc_us-gaap_InterestRateSwapMember_01a17520-7f6a-76b2-8754-96ae44476d0e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommodityContractMember_01a17520-7f6a-77d3-99a1-472aea35ed05" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommodityContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7f6a-7407-b59c-248bf82bde84" xlink:to="loc_us-gaap_CommodityContractMember_01a17520-7f6a-77d3-99a1-472aea35ed05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_01a17520-7f6a-79bf-a875-b50cc067f3f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a17520-7f6a-7934-99dc-e2fdb89c95cf" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_01a17520-7f6a-79bf-a875-b50cc067f3f8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_01a17520-7f6a-78e8-9117-87f7964f5c7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_01a17520-7f6a-79bf-a875-b50cc067f3f8" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_01a17520-7f6a-78e8-9117-87f7964f5c7c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_01a17520-7f6a-7af4-8557-a26220db2b40" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_01a17520-7f6a-79bf-a875-b50cc067f3f8" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_01a17520-7f6a-7af4-8557-a26220db2b40" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_01a17520-7f6a-73fa-a97a-dd6b1118ac35" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_01a17520-7f6a-79bf-a875-b50cc067f3f8" xlink:to="loc_us-gaap_DerivativeAssets_01a17520-7f6a-73fa-a97a-dd6b1118ac35" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_01a17520-7f6a-74c8-8c62-4acfc2d31177" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a17520-7f6a-7934-99dc-e2fdb89c95cf" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_01a17520-7f6a-74c8-8c62-4acfc2d31177" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_WarrantsFairValueDisclosure_01a17520-7f6a-7d4d-ab56-f23b8ae844bc" xlink:href="wdq-20260930.xsd#wdq_WarrantsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_01a17520-7f6a-74c8-8c62-4acfc2d31177" xlink:to="loc_wdq_WarrantsFairValueDisclosure_01a17520-7f6a-7d4d-ab56-f23b8ae844bc" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/RELATEDPARTIESRevenuesRecordedfromRelatedPartiesDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#RELATEDPARTIESRevenuesRecordedfromRelatedPartiesDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/RELATEDPARTIESRevenuesRecordedfromRelatedPartiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_01a17520-7f6a-7aae-badb-b67398bb0ea8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a17520-7f6a-7cc0-9196-ff27dcdfb7be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a17520-7f6a-7aae-badb-b67398bb0ea8" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a17520-7f6a-7cc0-9196-ff27dcdfb7be" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_01a17520-7f6a-7ff6-b77a-32542b1e77f0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a17520-7f6a-7cc0-9196-ff27dcdfb7be" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_01a17520-7f6a-7ff6-b77a-32542b1e77f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_01a17520-7f6a-7ff6-b77a-32542b1e77f0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_01a17520-7f6a-7ff6-b77a-32542b1e77f0" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_01a17520-7f6a-7ff6-b77a-32542b1e77f0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_01a17520-7f6a-715c-92c3-e376e0cf1799" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_01a17520-7f6a-7ff6-b77a-32542b1e77f0" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_01a17520-7f6a-715c-92c3-e376e0cf1799" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_EnvironmentalAttributesMember_01a17520-7f6a-7661-92f2-8f0561341b13" xlink:href="wdq-20260930.xsd#wdq_EnvironmentalAttributesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_01a17520-7f6a-715c-92c3-e376e0cf1799" xlink:to="loc_wdq_EnvironmentalAttributesMember_01a17520-7f6a-7661-92f2-8f0561341b13" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_CommoditySwapsMember_01a17520-7f6a-7030-a1ae-eecd77c7894f" xlink:href="wdq-20260930.xsd#wdq_CommoditySwapsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_01a17520-7f6a-715c-92c3-e376e0cf1799" xlink:to="loc_wdq_CommoditySwapsMember_01a17520-7f6a-7030-a1ae-eecd77c7894f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_EnvironmentalProcessingFeesMember_01a17520-7f6a-7b02-bc23-c1eb132820ec" xlink:href="wdq-20260930.xsd#wdq_EnvironmentalProcessingFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_01a17520-7f6a-715c-92c3-e376e0cf1799" xlink:to="loc_wdq_EnvironmentalProcessingFeesMember_01a17520-7f6a-7b02-bc23-c1eb132820ec" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7f6a-7e2a-ad2a-c29dc888d851" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a17520-7f6a-7cc0-9196-ff27dcdfb7be" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7f6a-7e2a-ad2a-c29dc888d851" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a17520-7f6a-7e2a-ad2a-c29dc888d851_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7f6a-7e2a-ad2a-c29dc888d851" xlink:to="loc_us-gaap_RelatedPartyDomain_01a17520-7f6a-7e2a-ad2a-c29dc888d851_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a17520-7f6a-79a7-8d4d-3f82578a19a4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7f6a-7e2a-ad2a-c29dc888d851" xlink:to="loc_us-gaap_RelatedPartyDomain_01a17520-7f6a-79a7-8d4d-3f82578a19a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a17520-7f6a-73c0-83fb-55865b957687" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a17520-7f6a-79a7-8d4d-3f82578a19a4" xlink:to="loc_us-gaap_RelatedPartyMember_01a17520-7f6a-73c0-83fb-55865b957687" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7f6a-7571-904d-063186c4ad07" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a17520-7f6a-7cc0-9196-ff27dcdfb7be" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7f6a-7571-904d-063186c4ad07" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a17520-7f6a-7571-904d-063186c4ad07_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7f6a-7571-904d-063186c4ad07" xlink:to="loc_us-gaap_SegmentDomain_01a17520-7f6a-7571-904d-063186c4ad07_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a17520-7f6a-7fef-954d-31b52e27744b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7f6a-7571-904d-063186c4ad07" xlink:to="loc_us-gaap_SegmentDomain_01a17520-7f6a-7fef-954d-31b52e27744b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RenewableNaturalGasFuelSupplySegmentMember_01a17520-7f6a-7ab3-adf9-8a8d567c9df2" xlink:href="wdq-20260930.xsd#wdq_RenewableNaturalGasFuelSupplySegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a17520-7f6a-7fef-954d-31b52e27744b" xlink:to="loc_wdq_RenewableNaturalGasFuelSupplySegmentMember_01a17520-7f6a-7ab3-adf9-8a8d567c9df2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_FuelStationServicesSegmentMember_01a17520-7f6a-7404-a709-f2e744214e1a" xlink:href="wdq-20260930.xsd#wdq_FuelStationServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a17520-7f6a-7fef-954d-31b52e27744b" xlink:to="loc_wdq_FuelStationServicesSegmentMember_01a17520-7f6a-7404-a709-f2e744214e1a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RenewablePowerSegmentMember_01a17520-7f6a-7b31-b458-d215961727b2" xlink:href="wdq-20260930.xsd#wdq_RenewablePowerSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a17520-7f6a-7fef-954d-31b52e27744b" xlink:to="loc_wdq_RenewablePowerSegmentMember_01a17520-7f6a-7b31-b458-d215961727b2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7f6a-7491-9386-c0577fbd12d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a17520-7f6a-7cc0-9196-ff27dcdfb7be" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7f6a-7491-9386-c0577fbd12d2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7f6a-7491-9386-c0577fbd12d2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7f6a-7491-9386-c0577fbd12d2" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7f6a-7491-9386-c0577fbd12d2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7f6a-78eb-9a30-58ebf4dce1d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a17520-7f6a-7491-9386-c0577fbd12d2" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7f6a-78eb-9a30-58ebf4dce1d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommodityContractMember_01a17520-7f6a-7822-bae7-2529b5a79bce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommodityContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a17520-7f6a-78eb-9a30-58ebf4dce1d4" xlink:to="loc_us-gaap_CommodityContractMember_01a17520-7f6a-7822-bae7-2529b5a79bce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_01a17520-7f6a-7f25-89d7-2e9190c1ca91" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a17520-7f6a-7aae-badb-b67398bb0ea8" xlink:to="loc_us-gaap_Revenues_01a17520-7f6a-7f25-89d7-2e9190c1ca91" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/RELATEDPARTIESNarrativeDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#RELATEDPARTIESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/RELATEDPARTIESNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_01a1c02a-6b63-7b8e-990b-c82b9da7d91f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a17520-7f6a-7ed1-bb60-86f890ebfe2f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a1c02a-6b63-7b8e-990b-c82b9da7d91f" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a17520-7f6a-7ed1-bb60-86f890ebfe2f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a1c032-3eaf-70cf-b73e-7c91c3347d1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a17520-7f6a-7ed1-bb60-86f890ebfe2f" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a1c032-3eaf-70cf-b73e-7c91c3347d1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a1c032-3eaf-70cf-b73e-7c91c3347d1d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a1c032-3eaf-70cf-b73e-7c91c3347d1d" xlink:to="loc_us-gaap_RelatedPartyDomain_01a1c032-3eaf-70cf-b73e-7c91c3347d1d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a1c032-3eaf-7627-9af7-daffc0b12f6b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a1c032-3eaf-70cf-b73e-7c91c3347d1d" xlink:to="loc_us-gaap_RelatedPartyDomain_01a1c032-3eaf-7627-9af7-daffc0b12f6b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a1c032-3eaf-7be6-87cb-455a49b3b59f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a1c032-3eaf-7627-9af7-daffc0b12f6b" xlink:to="loc_us-gaap_RelatedPartyMember_01a1c032-3eaf-7be6-87cb-455a49b3b59f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_01a1c10a-d2f9-7fa8-921d-1302d859bc96" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a17520-7f6a-7ed1-bb60-86f890ebfe2f" xlink:to="loc_srt_CounterpartyNameAxis_01a1c10a-d2f9-7fa8-921d-1302d859bc96" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a1c10a-d2f9-7fa8-921d-1302d859bc96_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_01a1c10a-d2f9-7fa8-921d-1302d859bc96" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a1c10a-d2f9-7fa8-921d-1302d859bc96_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a1c10a-d2f9-7ec1-ab91-8a45fb5ea55f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_01a1c10a-d2f9-7fa8-921d-1302d859bc96" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a1c10a-d2f9-7ec1-ab91-8a45fb5ea55f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_FortistarLLCFortistarMember_01a1c10a-d2f9-71e1-88d5-c930f615231c" xlink:href="wdq-20260930.xsd#wdq_FortistarLLCFortistarMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a1c10a-d2f9-7ec1-ab91-8a45fb5ea55f" xlink:to="loc_wdq_FortistarLLCFortistarMember_01a1c10a-d2f9-71e1-88d5-c930f615231c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_01a1c10a-63ba-73df-9c36-ea4b0eab02ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a1c02a-6b63-7b8e-990b-c82b9da7d91f" xlink:to="loc_us-gaap_Revenues_01a1c10a-63ba-73df-9c36-ea4b0eab02ef" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/RELATEDPARTIESVariousFeesRecordedUndertheAgreementsinSellingGeneralandAdministrativeExpensesAndRelatedPartiesDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#RELATEDPARTIESVariousFeesRecordedUndertheAgreementsinSellingGeneralandAdministrativeExpensesAndRelatedPartiesDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/RELATEDPARTIESVariousFeesRecordedUndertheAgreementsinSellingGeneralandAdministrativeExpensesAndRelatedPartiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_01a17520-7f6a-7457-aff0-696c58246ecd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a17520-7f6a-731b-9a44-6b12e00d8157" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a17520-7f6a-7457-aff0-696c58246ecd" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a17520-7f6a-731b-9a44-6b12e00d8157" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7f6a-7d33-ba38-e3e48426515a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a17520-7f6a-731b-9a44-6b12e00d8157" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7f6a-7d33-ba38-e3e48426515a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a17520-7f6a-7d33-ba38-e3e48426515a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7f6a-7d33-ba38-e3e48426515a" xlink:to="loc_us-gaap_RelatedPartyDomain_01a17520-7f6a-7d33-ba38-e3e48426515a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a17520-7f6a-7b37-9932-24f5a1889ba7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a17520-7f6a-7d33-ba38-e3e48426515a" xlink:to="loc_us-gaap_RelatedPartyDomain_01a17520-7f6a-7b37-9932-24f5a1889ba7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a17520-7f6a-785c-9a25-f477aff9df4e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a17520-7f6a-7b37-9932-24f5a1889ba7" xlink:to="loc_us-gaap_RelatedPartyMember_01a17520-7f6a-785c-9a25-f477aff9df4e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_01a17520-7f6a-7ed3-ab73-576ba7baf940" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a17520-7f6a-731b-9a44-6b12e00d8157" xlink:to="loc_srt_CounterpartyNameAxis_01a17520-7f6a-7ed3-ab73-576ba7baf940" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17520-7f6a-7ed3-ab73-576ba7baf940_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_01a17520-7f6a-7ed3-ab73-576ba7baf940" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17520-7f6a-7ed3-ab73-576ba7baf940_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17520-7f6a-7dd2-b103-209712843158" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_01a17520-7f6a-7ed3-ab73-576ba7baf940" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17520-7f6a-7dd2-b103-209712843158" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_CostarPartnersLLCCostarMember_01a17520-7f6a-71eb-be08-705c0cf402d1" xlink:href="wdq-20260930.xsd#wdq_CostarPartnersLLCCostarMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17520-7f6a-7dd2-b103-209712843158" xlink:to="loc_wdq_CostarPartnersLLCCostarMember_01a17520-7f6a-71eb-be08-705c0cf402d1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_NextEraMember_01a17520-7f6a-79ec-a1f5-c8d5535554a2" xlink:href="wdq-20260930.xsd#wdq_NextEraMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17520-7f6a-7dd2-b103-209712843158" xlink:to="loc_wdq_NextEraMember_01a17520-7f6a-79ec-a1f5-c8d5535554a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_OtherMember_01a17520-7f6a-77f8-98fc-324b9c6f0fa7" xlink:href="wdq-20260930.xsd#wdq_OtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17520-7f6a-7dd2-b103-209712843158" xlink:to="loc_wdq_OtherMember_01a17520-7f6a-77f8-98fc-324b9c6f0fa7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_EquityMethodInvestmentEntitiesMember_01a17520-7f6a-77ba-bc6a-fe417b59823e" xlink:href="wdq-20260930.xsd#wdq_EquityMethodInvestmentEntitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17520-7f6a-7dd2-b103-209712843158" xlink:to="loc_wdq_EquityMethodInvestmentEntitiesMember_01a17520-7f6a-77ba-bc6a-fe417b59823e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_01a17520-7f6a-7b1b-8e6d-4423aec35958" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a17520-7f6a-731b-9a44-6b12e00d8157" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_01a17520-7f6a-7b1b-8e6d-4423aec35958" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_01a17520-7f6a-7b1b-8e6d-4423aec35958_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_01a17520-7f6a-7b1b-8e6d-4423aec35958" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_01a17520-7f6a-7b1b-8e6d-4423aec35958_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_01a17520-7f6a-78fc-b9f4-a71ff034369a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_01a17520-7f6a-7b1b-8e6d-4423aec35958" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_01a17520-7f6a-78fc-b9f4-a71ff034369a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_StaffingAndManagementServicesMember_01a17520-7f6a-7fc2-a3f8-1d865c63cbd8" xlink:href="wdq-20260930.xsd#wdq_StaffingAndManagementServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_01a17520-7f6a-78fc-b9f4-a71ff034369a" xlink:to="loc_wdq_StaffingAndManagementServicesMember_01a17520-7f6a-7fc2-a3f8-1d865c63cbd8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RentFixedCompensationMember_01a17520-7f6a-793c-abb2-630a3dc6a31d" xlink:href="wdq-20260930.xsd#wdq_RentFixedCompensationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_01a17520-7f6a-78fc-b9f4-a71ff034369a" xlink:to="loc_wdq_RentFixedCompensationMember_01a17520-7f6a-793c-abb2-630a3dc6a31d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_ITServicesMember_01a17520-7f6a-7764-8b42-9db488ac8bf4" xlink:href="wdq-20260930.xsd#wdq_ITServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_01a17520-7f6a-78fc-b9f4-a71ff034369a" xlink:to="loc_wdq_ITServicesMember_01a17520-7f6a-7764-8b42-9db488ac8bf4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_01a17520-7f6a-700f-8af7-1f3baba483a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a17520-7f6a-7457-aff0-696c58246ecd" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_01a17520-7f6a-700f-8af7-1f3baba483a5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_01a17520-7f6a-7d2f-a046-c63372f12001" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a17520-7f6a-7457-aff0-696c58246ecd" xlink:to="loc_us-gaap_AssetsAbstract_01a17520-7f6a-7d2f-a046-c63372f12001" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableGrossCurrent_01a17520-7f6a-7cf1-bcbb-d25dfb614c2d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableGrossCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a17520-7f6a-7d2f-a046-c63372f12001" xlink:to="loc_us-gaap_AccountsReceivableGrossCurrent_01a17520-7f6a-7cf1-bcbb-d25dfb614c2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract_01a17520-7f6a-77ee-be22-902b1b64d7b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a17520-7f6a-7457-aff0-696c58246ecd" xlink:to="loc_us-gaap_LiabilitiesAbstract_01a17520-7f6a-77ee-be22-902b1b64d7b3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableOtherCurrent_01a17520-7f6a-799a-b0ff-73ca35164ba9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableOtherCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_01a17520-7f6a-77ee-be22-902b1b64d7b3" xlink:to="loc_us-gaap_AccountsPayableOtherCurrent_01a17520-7f6a-799a-b0ff-73ca35164ba9" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/REPORTABLESEGMENTSANDGEOGRAPHICINFORMATIONSegmentReportingInformationDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#REPORTABLESEGMENTSANDGEOGRAPHICINFORMATIONSegmentReportingInformationDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/REPORTABLESEGMENTSANDGEOGRAPHICINFORMATIONSegmentReportingInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_01a17520-7f6b-7b8d-bbc8-fc814f828075" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a17520-7f6b-706e-8c42-ba3181d366ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a17520-7f6b-7b8d-bbc8-fc814f828075" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a17520-7f6b-706e-8c42-ba3181d366ec" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7f6b-7c28-8c99-9efc8db190b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a17520-7f6b-706e-8c42-ba3181d366ec" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7f6b-7c28-8c99-9efc8db190b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a17520-7f6b-7c28-8c99-9efc8db190b2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7f6b-7c28-8c99-9efc8db190b2" xlink:to="loc_us-gaap_SegmentDomain_01a17520-7f6b-7c28-8c99-9efc8db190b2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a17520-7f6b-70c3-a63a-e00e5b2bac9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7f6b-7c28-8c99-9efc8db190b2" xlink:to="loc_us-gaap_SegmentDomain_01a17520-7f6b-70c3-a63a-e00e5b2bac9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RenewableNaturalGasFuelSupplySegmentMember_01a17520-7f6b-7094-a23a-82aa97697c72" xlink:href="wdq-20260930.xsd#wdq_RenewableNaturalGasFuelSupplySegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a17520-7f6b-70c3-a63a-e00e5b2bac9d" xlink:to="loc_wdq_RenewableNaturalGasFuelSupplySegmentMember_01a17520-7f6b-7094-a23a-82aa97697c72" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_FuelStationServicesSegmentMember_01a17520-7f6b-79bd-a9f9-479439a38bf9" xlink:href="wdq-20260930.xsd#wdq_FuelStationServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a17520-7f6b-70c3-a63a-e00e5b2bac9d" xlink:to="loc_wdq_FuelStationServicesSegmentMember_01a17520-7f6b-79bd-a9f9-479439a38bf9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RenewablePowerSegmentMember_01a17520-7f6b-7b88-98a6-9cad1f14df95" xlink:href="wdq-20260930.xsd#wdq_RenewablePowerSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a17520-7f6b-70c3-a63a-e00e5b2bac9d" xlink:to="loc_wdq_RenewablePowerSegmentMember_01a17520-7f6b-7b88-98a6-9cad1f14df95" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_01a17520-7f6b-7a21-af11-3cd62acf0f76" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a17520-7f6b-706e-8c42-ba3181d366ec" xlink:to="loc_srt_ConsolidationItemsAxis_01a17520-7f6b-7a21-af11-3cd62acf0f76" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a17520-7f6b-7a21-af11-3cd62acf0f76_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_01a17520-7f6b-7a21-af11-3cd62acf0f76" xlink:to="loc_srt_ConsolidationItemsDomain_01a17520-7f6b-7a21-af11-3cd62acf0f76_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a17520-7f6b-7767-baeb-591dbdcd95cb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_01a17520-7f6b-7a21-af11-3cd62acf0f76" xlink:to="loc_srt_ConsolidationItemsDomain_01a17520-7f6b-7767-baeb-591dbdcd95cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntersegmentEliminationMember_01a17520-7f6b-78f6-a183-76f0d222d2a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntersegmentEliminationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_01a17520-7f6b-7767-baeb-591dbdcd95cb" xlink:to="loc_us-gaap_IntersegmentEliminationMember_01a17520-7f6b-78f6-a183-76f0d222d2a3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_01a17520-7f6b-79cc-ba03-a40c5d1e1593" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_01a17520-7f6b-7767-baeb-591dbdcd95cb" xlink:to="loc_us-gaap_OperatingSegmentsMember_01a17520-7f6b-79cc-ba03-a40c5d1e1593" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_01a17520-7f6b-7efa-88fb-274f774cf524" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_01a17520-7f6b-7767-baeb-591dbdcd95cb" xlink:to="loc_us-gaap_CorporateNonSegmentMember_01a17520-7f6b-7efa-88fb-274f774cf524" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_CorporateAndEliminationsMember_01a17520-7f6b-7a87-87f0-400107aae0d5" xlink:href="wdq-20260930.xsd#wdq_CorporateAndEliminationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_01a17520-7f6b-7767-baeb-591dbdcd95cb" xlink:to="loc_wdq_CorporateAndEliminationsMember_01a17520-7f6b-7a87-87f0-400107aae0d5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsAxis_01a17520-7f6b-75b1-a2ed-3cf76d8d3f2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a17520-7f6b-706e-8c42-ba3181d366ec" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsAxis_01a17520-7f6b-75b1-a2ed-3cf76d8d3f2e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsDomain_01a17520-7f6b-75b1-a2ed-3cf76d8d3f2e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsegmentsConsolidationItemsAxis_01a17520-7f6b-75b1-a2ed-3cf76d8d3f2e" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsDomain_01a17520-7f6b-75b1-a2ed-3cf76d8d3f2e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsDomain_01a17520-7f6b-7401-81ff-851d80c95279" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsegmentsConsolidationItemsAxis_01a17520-7f6b-75b1-a2ed-3cf76d8d3f2e" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsDomain_01a17520-7f6b-7401-81ff-851d80c95279" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntersubsegmentEliminationsMember_01a17520-7f6b-7168-a064-ed188faa5ed8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntersubsegmentEliminationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsConsolidationItemsDomain_01a17520-7f6b-7401-81ff-851d80c95279" xlink:to="loc_us-gaap_IntersubsegmentEliminationsMember_01a17520-7f6b-7168-a064-ed188faa5ed8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_01a17520-7f6b-737a-b947-58ca1910c6d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a17520-7f6b-7b8d-bbc8-fc814f828075" xlink:to="loc_us-gaap_Revenues_01a17520-7f6b-737a-b947-58ca1910c6d1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_CostOfGoodsAndServicesSoldAndOtherOperatingExpenses_01a17520-7f6b-7d84-babf-60d596319f89" xlink:href="wdq-20260930.xsd#wdq_CostOfGoodsAndServicesSoldAndOtherOperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a17520-7f6b-7b8d-bbc8-fc814f828075" xlink:to="loc_wdq_CostOfGoodsAndServicesSoldAndOtherOperatingExpenses_01a17520-7f6b-7d84-babf-60d596319f89" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_01a17520-7f6b-7821-aeb6-a12024a1e22f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a17520-7f6b-7b8d-bbc8-fc814f828075" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_01a17520-7f6b-7821-aeb6-a12024a1e22f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_InterestAndFinancingExpenseNet_01a17520-7f6b-7c93-a940-f68505beadf7" xlink:href="wdq-20260930.xsd#wdq_InterestAndFinancingExpenseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a17520-7f6b-7b8d-bbc8-fc814f828075" xlink:to="loc_wdq_InterestAndFinancingExpenseNet_01a17520-7f6b-7c93-a940-f68505beadf7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_01a17520-7f6b-7c73-8583-664ba20a7608" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a17520-7f6b-7b8d-bbc8-fc814f828075" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_01a17520-7f6b-7c73-8583-664ba20a7608" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TangibleAssetImpairmentCharges_01a17520-7f6b-7aff-b658-8e785fa5f761" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TangibleAssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a17520-7f6b-7b8d-bbc8-fc814f828075" xlink:to="loc_us-gaap_TangibleAssetImpairmentCharges_01a17520-7f6b-7aff-b658-8e785fa5f761" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAmortizationAndAccretionNet_01a17520-7f6b-7108-bbd3-85ab5f74f3df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationAmortizationAndAccretionNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a17520-7f6b-7b8d-bbc8-fc814f828075" xlink:to="loc_us-gaap_DepreciationAmortizationAndAccretionNet_01a17520-7f6b-7108-bbd3-85ab5f74f3df" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_OtherCorporateExpenses_01a17520-7f6b-7dd6-a1ba-ccd47fcbdb34" xlink:href="wdq-20260930.xsd#wdq_OtherCorporateExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a17520-7f6b-7b8d-bbc8-fc814f828075" xlink:to="loc_wdq_OtherCorporateExpenses_01a17520-7f6b-7dd6-a1ba-ccd47fcbdb34" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeBenefitsAndShareBasedCompensation_01a17520-7f6b-74b8-afd9-190980c1ca39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeBenefitsAndShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a17520-7f6b-7b8d-bbc8-fc814f828075" xlink:to="loc_us-gaap_EmployeeBenefitsAndShareBasedCompensation_01a17520-7f6b-74b8-afd9-190980c1ca39" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_01a17520-7f6b-7407-8d2b-02abfce41a1a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a17520-7f6b-7b8d-bbc8-fc814f828075" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_01a17520-7f6b-7407-8d2b-02abfce41a1a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a17520-7f6b-7414-b26f-eae6c97b3c51" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a17520-7f6b-7b8d-bbc8-fc814f828075" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a17520-7f6b-7414-b26f-eae6c97b3c51" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_01a17520-7f6b-7791-b1e2-5cf9d9b2d627" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a17520-7f6b-7b8d-bbc8-fc814f828075" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_01a17520-7f6b-7791-b1e2-5cf9d9b2d627" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_01a17520-7f6b-7e7d-ad28-9d05bb6a5ceb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a17520-7f6b-7b8d-bbc8-fc814f828075" xlink:to="loc_us-gaap_ProfitLoss_01a17520-7f6b-7e7d-ad28-9d05bb6a5ceb" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_01a17520-7f6b-76d2-8102-2c8e2996b1e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a17520-7f6b-7b8d-bbc8-fc814f828075" xlink:to="loc_us-gaap_EquityMethodInvestments_01a17520-7f6b-76d2-8102-2c8e2996b1e9" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_01a17520-7f6b-7625-85ec-34d9dd50a4cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a17520-7f6b-7b8d-bbc8-fc814f828075" xlink:to="loc_us-gaap_Assets_01a17520-7f6b-7625-85ec-34d9dd50a4cb" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_01a17520-7f6b-74ad-b192-cba8e37132d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentExpenditureAdditionToLongLivedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a17520-7f6b-7b8d-bbc8-fc814f828075" xlink:to="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_01a17520-7f6b-74ad-b192-cba8e37132d5" xlink:type="arc" order="15"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/REPORTABLESEGMENTSANDGEOGRAPHICINFORMATIONRevenuebyMajorCustomerbyReportingSegmentDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#REPORTABLESEGMENTSANDGEOGRAPHICINFORMATIONRevenuebyMajorCustomerbyReportingSegmentDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/REPORTABLESEGMENTSANDGEOGRAPHICINFORMATIONRevenuebyMajorCustomerbyReportingSegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EntityWideRevenueMajorCustomerLineItems_01a17520-7f6b-72f4-ac34-29e98c00b6f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EntityWideRevenueMajorCustomerLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_01a17520-7f6b-744f-8158-45d7e9ea0861" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EntityWideRevenueMajorCustomerLineItems_01a17520-7f6b-72f4-ac34-29e98c00b6f8" xlink:to="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_01a17520-7f6b-744f-8158-45d7e9ea0861" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_01a17520-7f6b-723d-ae70-0a3984dc311b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_01a17520-7f6b-744f-8158-45d7e9ea0861" xlink:to="loc_srt_ProductOrServiceAxis_01a17520-7f6b-723d-ae70-0a3984dc311b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a17520-7f6b-723d-ae70-0a3984dc311b_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_01a17520-7f6b-723d-ae70-0a3984dc311b" xlink:to="loc_srt_ProductsAndServicesDomain_01a17520-7f6b-723d-ae70-0a3984dc311b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a17520-7f6b-745a-ac4b-19c937e4aabe" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_01a17520-7f6b-723d-ae70-0a3984dc311b" xlink:to="loc_srt_ProductsAndServicesDomain_01a17520-7f6b-745a-ac4b-19c937e4aabe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_EnvironmentalAttributesMember_01a17520-7f6b-74cc-aca0-bc1095d2f22e" xlink:href="wdq-20260930.xsd#wdq_EnvironmentalAttributesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a17520-7f6b-745a-ac4b-19c937e4aabe" xlink:to="loc_wdq_EnvironmentalAttributesMember_01a17520-7f6b-74cc-aca0-bc1095d2f22e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_BrownGasSalesAndOtherMember_01a17520-7f6b-766a-b07d-f12bb0c5e310" xlink:href="wdq-20260930.xsd#wdq_BrownGasSalesAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a17520-7f6b-745a-ac4b-19c937e4aabe" xlink:to="loc_wdq_BrownGasSalesAndOtherMember_01a17520-7f6b-766a-b07d-f12bb0c5e310" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_OPALOwnedStationsMember_01a17520-7f6b-7482-8004-46a3698be44c" xlink:href="wdq-20260930.xsd#wdq_OPALOwnedStationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a17520-7f6b-745a-ac4b-19c937e4aabe" xlink:to="loc_wdq_OPALOwnedStationsMember_01a17520-7f6b-7482-8004-46a3698be44c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_EnvironmentalAttributesAndRNGMarketingMember_01a17520-7f6b-72cb-8ca5-76e6b9796d8f" xlink:href="wdq-20260930.xsd#wdq_EnvironmentalAttributesAndRNGMarketingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a17520-7f6b-745a-ac4b-19c937e4aabe" xlink:to="loc_wdq_EnvironmentalAttributesAndRNGMarketingMember_01a17520-7f6b-72cb-8ca5-76e6b9796d8f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_ThirdPartyStationServiceAndMaintenanceMember_01a17520-7f6b-79f4-bbfd-d26d16733ab7" xlink:href="wdq-20260930.xsd#wdq_ThirdPartyStationServiceAndMaintenanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a17520-7f6b-745a-ac4b-19c937e4aabe" xlink:to="loc_wdq_ThirdPartyStationServiceAndMaintenanceMember_01a17520-7f6b-79f4-bbfd-d26d16733ab7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionMember_01a17520-7f6b-78f0-95aa-0f912356ba59" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConstructionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a17520-7f6b-745a-ac4b-19c937e4aabe" xlink:to="loc_us-gaap_ConstructionMember_01a17520-7f6b-78f0-95aa-0f912356ba59" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_LeaseRevenuesMember_01a17520-7f6b-7bc0-9eb0-dbbe6d762a8a" xlink:href="wdq-20260930.xsd#wdq_LeaseRevenuesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a17520-7f6b-745a-ac4b-19c937e4aabe" xlink:to="loc_wdq_LeaseRevenuesMember_01a17520-7f6b-7bc0-9eb0-dbbe6d762a8a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_ElectricitySalesMember_01a17520-7f6b-783c-b918-78637b3962a0" xlink:href="wdq-20260930.xsd#wdq_ElectricitySalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a17520-7f6b-745a-ac4b-19c937e4aabe" xlink:to="loc_wdq_ElectricitySalesMember_01a17520-7f6b-783c-b918-78637b3962a0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_OtherMember_01a17520-7f6b-715a-9f34-714105d8b87e" xlink:href="wdq-20260930.xsd#wdq_OtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a17520-7f6b-745a-ac4b-19c937e4aabe" xlink:to="loc_wdq_OtherMember_01a17520-7f6b-715a-9f34-714105d8b87e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7f6b-72d6-89b6-57f24f0e4769" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_01a17520-7f6b-744f-8158-45d7e9ea0861" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7f6b-72d6-89b6-57f24f0e4769" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a17520-7f6b-72d6-89b6-57f24f0e4769_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7f6b-72d6-89b6-57f24f0e4769" xlink:to="loc_us-gaap_SegmentDomain_01a17520-7f6b-72d6-89b6-57f24f0e4769_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a17520-7f6b-7147-9880-6391db87e42c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a17520-7f6b-72d6-89b6-57f24f0e4769" xlink:to="loc_us-gaap_SegmentDomain_01a17520-7f6b-7147-9880-6391db87e42c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RenewableNaturalGasFuelSupplySegmentMember_01a17520-7f6b-7b3a-9233-2f88021de486" xlink:href="wdq-20260930.xsd#wdq_RenewableNaturalGasFuelSupplySegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a17520-7f6b-7147-9880-6391db87e42c" xlink:to="loc_wdq_RenewableNaturalGasFuelSupplySegmentMember_01a17520-7f6b-7b3a-9233-2f88021de486" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_FuelStationServicesSegmentMember_01a17520-7f6b-7092-950a-c842613543ed" xlink:href="wdq-20260930.xsd#wdq_FuelStationServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a17520-7f6b-7147-9880-6391db87e42c" xlink:to="loc_wdq_FuelStationServicesSegmentMember_01a17520-7f6b-7092-950a-c842613543ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RenewablePowerSegmentMember_01a17520-7f6b-7a0a-a1a9-d21c4161b9f9" xlink:href="wdq-20260930.xsd#wdq_RenewablePowerSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a17520-7f6b-7147-9880-6391db87e42c" xlink:to="loc_wdq_RenewablePowerSegmentMember_01a17520-7f6b-7a0a-a1a9-d21c4161b9f9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_01a17520-7f6b-79a0-8ae3-daf1909b469a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_01a17520-7f6b-744f-8158-45d7e9ea0861" xlink:to="loc_srt_CounterpartyNameAxis_01a17520-7f6b-79a0-8ae3-daf1909b469a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17520-7f6b-79a0-8ae3-daf1909b469a_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_01a17520-7f6b-79a0-8ae3-daf1909b469a" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17520-7f6b-79a0-8ae3-daf1909b469a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17520-7f6b-7173-8321-9a3bf3c2e178" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_01a17520-7f6b-79a0-8ae3-daf1909b469a" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17520-7f6b-7173-8321-9a3bf3c2e178" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_OCIFuelsB.V.OCIMember_01a17520-7f6b-7837-a698-89a0a005301f" xlink:href="wdq-20260930.xsd#wdq_OCIFuelsB.V.OCIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17520-7f6b-7173-8321-9a3bf3c2e178" xlink:to="loc_wdq_OCIFuelsB.V.OCIMember_01a17520-7f6b-7837-a698-89a0a005301f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_01a17520-7f6b-748c-9af2-c6e95bee0db3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_01a17520-7f6b-744f-8158-45d7e9ea0861" xlink:to="loc_srt_MajorCustomersAxis_01a17520-7f6b-748c-9af2-c6e95bee0db3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_01a17520-7f6b-748c-9af2-c6e95bee0db3_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_01a17520-7f6b-748c-9af2-c6e95bee0db3" xlink:to="loc_srt_NameOfMajorCustomerDomain_01a17520-7f6b-748c-9af2-c6e95bee0db3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_01a17520-7f6b-717b-99ce-049290fdd8df" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_01a17520-7f6b-748c-9af2-c6e95bee0db3" xlink:to="loc_srt_NameOfMajorCustomerDomain_01a17520-7f6b-717b-99ce-049290fdd8df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_CustomerAMember_01a17520-7f6b-7f5d-94e7-b26a05d171a8" xlink:href="wdq-20260930.xsd#wdq_CustomerAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_01a17520-7f6b-717b-99ce-049290fdd8df" xlink:to="loc_wdq_CustomerAMember_01a17520-7f6b-7f5d-94e7-b26a05d171a8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_01a17520-7f6b-76bd-ab22-5a682a2178a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_01a17520-7f6b-744f-8158-45d7e9ea0861" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_01a17520-7f6b-76bd-ab22-5a682a2178a8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a17520-7f6b-76bd-ab22-5a682a2178a8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a17520-7f6b-76bd-ab22-5a682a2178a8" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a17520-7f6b-76bd-ab22-5a682a2178a8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a17520-7f6b-759c-9093-29d367fa5e1a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a17520-7f6b-76bd-ab22-5a682a2178a8" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a17520-7f6b-759c-9093-29d367fa5e1a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_01a17520-7f6b-7886-b604-6cc8773d4797" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_01a17520-7f6b-759c-9093-29d367fa5e1a" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_01a17520-7f6b-7886-b604-6cc8773d4797" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a17520-7f6b-7115-bb3b-943d5e54c994" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_01a17520-7f6b-744f-8158-45d7e9ea0861" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a17520-7f6b-7115-bb3b-943d5e54c994" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a17520-7f6b-7115-bb3b-943d5e54c994_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a17520-7f6b-7115-bb3b-943d5e54c994" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a17520-7f6b-7115-bb3b-943d5e54c994_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a17520-7f6b-73a8-ae63-ed3f641b24db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a17520-7f6b-7115-bb3b-943d5e54c994" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a17520-7f6b-73a8-ae63-ed3f641b24db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_01a17520-7f6b-7a25-bcb8-5e4037e857b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a17520-7f6b-73a8-ae63-ed3f641b24db" xlink:to="loc_us-gaap_SalesRevenueNetMember_01a17520-7f6b-7a25-bcb8-5e4037e857b1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_01a17520-7f6b-72aa-bac0-f7b08e979efc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideRevenueMajorCustomerLineItems_01a17520-7f6b-72f4-ac34-29e98c00b6f8" xlink:to="loc_us-gaap_Revenues_01a17520-7f6b-72aa-bac0-f7b08e979efc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a17520-7f6b-7442-bdae-887433269746" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideRevenueMajorCustomerLineItems_01a17520-7f6b-72f4-ac34-29e98c00b6f8" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a17520-7f6b-7442-bdae-887433269746" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueNotFromContractWithCustomer_01a17520-7f6b-7e49-951c-c4738f246010" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueNotFromContractWithCustomer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideRevenueMajorCustomerLineItems_01a17520-7f6b-72f4-ac34-29e98c00b6f8" xlink:to="loc_us-gaap_RevenueNotFromContractWithCustomer_01a17520-7f6b-7e49-951c-c4738f246010" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_01a17520-7f6b-7239-b483-a38467f2c011" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideRevenueMajorCustomerLineItems_01a17520-7f6b-72f4-ac34-29e98c00b6f8" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_01a17520-7f6b-7239-b483-a38467f2c011" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/REDEEMABLENONCONTROLLINGINTERESTREDEEMABLEPREFERREDNONCONTROLLINGINTERESTANDSTOCKHOLDERSEQUITYNarrativeDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#REDEEMABLENONCONTROLLINGINTERESTREDEEMABLEPREFERREDNONCONTROLLINGINTERESTANDSTOCKHOLDERSEQUITYNarrativeDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/REDEEMABLENONCONTROLLINGINTERESTREDEEMABLEPREFERREDNONCONTROLLINGINTERESTANDSTOCKHOLDERSEQUITYNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredUnitsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPreferredUnitsTable_01a17520-7f6b-74a3-836f-e4a863f35dd9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPreferredUnitsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_us-gaap_ScheduleOfPreferredUnitsTable_01a17520-7f6b-74a3-836f-e4a863f35dd9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_01a17520-7f6b-7cdf-8f61-8f106ed7b3fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPreferredUnitsTable_01a17520-7f6b-74a3-836f-e4a863f35dd9" xlink:to="loc_us-gaap_StatementClassOfStockAxis_01a17520-7f6b-7cdf-8f61-8f106ed7b3fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a17520-7f6b-7cdf-8f61-8f106ed7b3fc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a17520-7f6b-7cdf-8f61-8f106ed7b3fc" xlink:to="loc_us-gaap_ClassOfStockDomain_01a17520-7f6b-7cdf-8f61-8f106ed7b3fc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a17520-7f6b-7182-acc4-a3cce41ca40e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a17520-7f6b-7cdf-8f61-8f106ed7b3fc" xlink:to="loc_us-gaap_ClassOfStockDomain_01a17520-7f6b-7182-acc4-a3cce41ca40e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_01a17520-7f6b-7490-98c6-73310c2eff31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7f6b-7182-acc4-a3cce41ca40e" xlink:to="loc_us-gaap_CommonClassAMember_01a17520-7f6b-7490-98c6-73310c2eff31" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_01a17520-7f6b-7a36-b45a-867a5b89fec2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7f6b-7182-acc4-a3cce41ca40e" xlink:to="loc_us-gaap_CommonClassBMember_01a17520-7f6b-7a36-b45a-867a5b89fec2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassCMember_01a17520-7f6b-7bf4-ba64-dd7c0e432595" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7f6b-7182-acc4-a3cce41ca40e" xlink:to="loc_us-gaap_CommonClassCMember_01a17520-7f6b-7bf4-ba64-dd7c0e432595" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_CommonClassDMember_01a17520-7f6b-79e3-b8c5-6ca439d4fb8a" xlink:href="wdq-20260930.xsd#wdq_CommonClassDMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7f6b-7182-acc4-a3cce41ca40e" xlink:to="loc_wdq_CommonClassDMember_01a17520-7f6b-79e3-b8c5-6ca439d4fb8a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_01a17520-7f6b-7f1a-ae25-45282d2a68f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7f6b-7182-acc4-a3cce41ca40e" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_01a17520-7f6b-7f1a-ae25-45282d2a68f9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_SeriesA1PreferredStockMember_01a17520-7f6b-73ba-bdbe-0b1559504ba3" xlink:href="wdq-20260930.xsd#wdq_SeriesA1PreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7f6b-7182-acc4-a3cce41ca40e" xlink:to="loc_wdq_SeriesA1PreferredStockMember_01a17520-7f6b-73ba-bdbe-0b1559504ba3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_01a17520-7f6b-717f-9354-d6cb665334aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPreferredUnitsTable_01a17520-7f6b-74a3-836f-e4a863f35dd9" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_01a17520-7f6b-717f-9354-d6cb665334aa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a17520-7f6b-717f-9354-d6cb665334aa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_01a17520-7f6b-717f-9354-d6cb665334aa" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a17520-7f6b-717f-9354-d6cb665334aa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a17520-7f6b-7bf3-b3e4-37aca8d98b0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_01a17520-7f6b-717f-9354-d6cb665334aa" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a17520-7f6b-7bf3-b3e4-37aca8d98b0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_SubscriptionAgreementMember_01a17520-7f6b-79ff-a35d-3e17e9d00aa5" xlink:href="wdq-20260930.xsd#wdq_SubscriptionAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a17520-7f6b-7bf3-b3e4-37aca8d98b0c" xlink:to="loc_wdq_SubscriptionAgreementMember_01a17520-7f6b-79ff-a35d-3e17e9d00aa5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_01a17520-7f6b-7647-ba1a-a38df6669a66" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPreferredUnitsTable_01a17520-7f6b-74a3-836f-e4a863f35dd9" xlink:to="loc_dei_LegalEntityAxis_01a17520-7f6b-7647-ba1a-a38df6669a66" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a17520-7f6b-7647-ba1a-a38df6669a66_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_01a17520-7f6b-7647-ba1a-a38df6669a66" xlink:to="loc_dei_EntityDomain_01a17520-7f6b-7647-ba1a-a38df6669a66_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a17520-7f6b-7e37-9b3b-d94429618f53" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_01a17520-7f6b-7647-ba1a-a38df6669a66" xlink:to="loc_dei_EntityDomain_01a17520-7f6b-7e37-9b3b-d94429618f53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_PreferredFuelsMember_01a17520-7f6b-75b0-b076-bf2a3ae1fc72" xlink:href="wdq-20260930.xsd#wdq_PreferredFuelsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01a17520-7f6b-7e37-9b3b-d94429618f53" xlink:to="loc_wdq_PreferredFuelsMember_01a17520-7f6b-75b0-b076-bf2a3ae1fc72" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_01a17520-7f6b-7875-bd2d-29d2c84684d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPreferredUnitsTable_01a17520-7f6b-74a3-836f-e4a863f35dd9" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_01a17520-7f6b-7875-bd2d-29d2c84684d4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a17520-7f6b-7875-bd2d-29d2c84684d4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a17520-7f6b-7875-bd2d-29d2c84684d4" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a17520-7f6b-7875-bd2d-29d2c84684d4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a17520-7f6b-7c2e-be1b-705825bad5fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a17520-7f6b-7875-bd2d-29d2c84684d4" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a17520-7f6b-7c2e-be1b-705825bad5fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_PreferredFuelsMember_01a17520-7f6b-7c9b-a5bb-43852df49513" xlink:href="wdq-20260930.xsd#wdq_PreferredFuelsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a17520-7f6b-7c2e-be1b-705825bad5fd" xlink:to="loc_wdq_PreferredFuelsMember_01a17520-7f6b-7c9b-a5bb-43852df49513" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_PreferredFuelsContingentWarrantsMember_01a17520-7f6b-7a0b-bda4-5c8044947d0b" xlink:href="wdq-20260930.xsd#wdq_PreferredFuelsContingentWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a17520-7f6b-7c2e-be1b-705825bad5fd" xlink:to="loc_wdq_PreferredFuelsContingentWarrantsMember_01a17520-7f6b-7a0b-bda4-5c8044947d0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_01a17520-7f6b-7e86-9963-8f49291c9cb9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_01a17520-7f6b-7e86-9963-8f49291c9cb9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues_01a17520-7f6b-7596-991f-4084a289ebf6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues_01a17520-7f6b-7596-991f-4084a289ebf6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_01a17520-7f6b-7a03-9759-2a1f999e8fce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_01a17520-7f6b-7a03-9759-2a1f999e8fce" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_01a17520-7f6b-7388-8a7e-4a1a7b0455e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_01a17520-7f6b-7388-8a7e-4a1a7b0455e9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_SaleOfStockUndrawnCommitment_01a17520-7f6b-713a-841b-222d0def6402" xlink:href="wdq-20260930.xsd#wdq_SaleOfStockUndrawnCommitment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_wdq_SaleOfStockUndrawnCommitment_01a17520-7f6b-713a-841b-222d0def6402" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_SaleOfStockAvailabilityPeriod_01a17520-7f6b-7506-832c-18046f7d5556" xlink:href="wdq-20260930.xsd#wdq_SaleOfStockAvailabilityPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_wdq_SaleOfStockAvailabilityPeriod_01a17520-7f6b-7506-832c-18046f7d5556" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_SaleOfStockMaximumNumberOfAdditionalSharesIssuedInTransaction_01a17520-7f6b-7290-a5aa-21c4585a7ac2" xlink:href="wdq-20260930.xsd#wdq_SaleOfStockMaximumNumberOfAdditionalSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_wdq_SaleOfStockMaximumNumberOfAdditionalSharesIssuedInTransaction_01a17520-7f6b-7290-a5aa-21c4585a7ac2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_SaleOfStockAggregatePrice_01a17520-7f6b-7fb1-91fe-71f172d42d35" xlink:href="wdq-20260930.xsd#wdq_SaleOfStockAggregatePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_wdq_SaleOfStockAggregatePrice_01a17520-7f6b-7fb1-91fe-71f172d42d35" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_SaleOfStockAdditionalUnitsMaximumPeriod_01a17520-7f6b-7d10-a325-fd3146b6308b" xlink:href="wdq-20260930.xsd#wdq_SaleOfStockAdditionalUnitsMaximumPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_wdq_SaleOfStockAdditionalUnitsMaximumPeriod_01a17520-7f6b-7d10-a325-fd3146b6308b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_01a17520-7f6b-783b-8166-eae5f297df5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_01a17520-7f6b-783b-8166-eae5f297df5b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_01a17520-7f6b-7d81-a100-8d0124d1b62f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_01a17520-7f6b-7d81-a100-8d0124d1b62f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_ClassOfWarrantOrRightOwnershipPercentageThreshold_01a17520-7f6b-74cf-beb8-b687ff8fab3b" xlink:href="wdq-20260930.xsd#wdq_ClassOfWarrantOrRightOwnershipPercentageThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_wdq_ClassOfWarrantOrRightOwnershipPercentageThreshold_01a17520-7f6b-74cf-beb8-b687ff8fab3b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_01a17520-7f6b-7d79-be54-c481d63074af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_01a17520-7f6b-7d79-be54-c481d63074af" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_01a17520-7f6b-73c8-964a-f208f7af51b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_01a17520-7f6b-73c8-964a-f208f7af51b6" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_WarrantsFairValueDisclosure_01a17520-7f6b-78d1-a6da-0966c482a041" xlink:href="wdq-20260930.xsd#wdq_WarrantsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_wdq_WarrantsFairValueDisclosure_01a17520-7f6b-78d1-a6da-0966c482a041" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_01a17520-7f6b-746a-b0fa-3095706ddcb1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_01a17520-7f6b-746a-b0fa-3095706ddcb1" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockDividendRatePercentage_01a17520-7f6b-7466-8157-21ba65044758" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockDividendRatePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_us-gaap_PreferredStockDividendRatePercentage_01a17520-7f6b-7466-8157-21ba65044758" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_PreferredStockPaymentInKindPercentage_01a17520-7f6b-7d7c-a3fe-2ca5fc107800" xlink:href="wdq-20260930.xsd#wdq_PreferredStockPaymentInKindPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_wdq_PreferredStockPaymentInKindPercentage_01a17520-7f6b-7d7c-a3fe-2ca5fc107800" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockRedemptionPricePerShare_01a17520-7f6b-72b5-a940-2785bcaa6766" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockRedemptionPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_us-gaap_PreferredStockRedemptionPricePerShare_01a17520-7f6b-72b5-a940-2785bcaa6766" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_PreferredStockRedemptionFailureCurePeriodDays_01a17520-7f6b-794f-af8e-44ac785ae9cb" xlink:href="wdq-20260930.xsd#wdq_PreferredStockRedemptionFailureCurePeriodDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_wdq_PreferredStockRedemptionFailureCurePeriodDays_01a17520-7f6b-794f-af8e-44ac785ae9cb" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_PreferredStockCovenantRemediationPeriod_01a17520-7f6b-7bfd-aa0e-63023ee17cc9" xlink:href="wdq-20260930.xsd#wdq_PreferredStockCovenantRemediationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_wdq_PreferredStockCovenantRemediationPeriod_01a17520-7f6b-7bfd-aa0e-63023ee17cc9" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_PreferredDividendPenaltyIncreaseDecreaseInQuarterlyPeriodPercentage_01a17520-7f6b-78a1-983a-9ff66cb2a09b" xlink:href="wdq-20260930.xsd#wdq_PreferredDividendPenaltyIncreaseDecreaseInQuarterlyPeriodPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_wdq_PreferredDividendPenaltyIncreaseDecreaseInQuarterlyPeriodPercentage_01a17520-7f6b-78a1-983a-9ff66cb2a09b" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_PreferredDividendMaximumPenaltyRateAnnualPercentage_01a17520-7f6b-7327-891d-594555fea55a" xlink:href="wdq-20260930.xsd#wdq_PreferredDividendMaximumPenaltyRateAnnualPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_wdq_PreferredDividendMaximumPenaltyRateAnnualPercentage_01a17520-7f6b-7327-891d-594555fea55a" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_PreferredStockRedemptionPriceRatio_01a17520-7f6b-7f19-afde-459fea922c46" xlink:href="wdq-20260930.xsd#wdq_PreferredStockRedemptionPriceRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_wdq_PreferredStockRedemptionPriceRatio_01a17520-7f6b-7f19-afde-459fea922c46" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_PreferredStockRedemptionPricePercentage_01a17520-7f6b-7bec-b462-769fbb768828" xlink:href="wdq-20260930.xsd#wdq_PreferredStockRedemptionPricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-737c-9152-be5656070385" xlink:to="loc_wdq_PreferredStockRedemptionPricePercentage_01a17520-7f6b-7bec-b462-769fbb768828" xlink:type="arc" order="24"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/REDEEMABLENONCONTROLLINGINTERESTREDEEMABLEPREFERREDNONCONTROLLINGINTERESTANDSTOCKHOLDERSEQUITYChangesinRedeemablePreferredUnitsDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#REDEEMABLENONCONTROLLINGINTERESTREDEEMABLEPREFERREDNONCONTROLLINGINTERESTANDSTOCKHOLDERSEQUITYChangesinRedeemablePreferredUnitsDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/REDEEMABLENONCONTROLLINGINTERESTREDEEMABLEPREFERREDNONCONTROLLINGINTERESTANDSTOCKHOLDERSEQUITYChangesinRedeemablePreferredUnitsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-73fe-ba43-fe82040c60fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredUnitsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPreferredUnitsTable_01a17520-7f6b-78e6-afb5-191ab4cb9a48" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPreferredUnitsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-73fe-ba43-fe82040c60fc" xlink:to="loc_us-gaap_ScheduleOfPreferredUnitsTable_01a17520-7f6b-78e6-afb5-191ab4cb9a48" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_01a17520-7f6b-7264-a222-1454ba6a1d08" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPreferredUnitsTable_01a17520-7f6b-78e6-afb5-191ab4cb9a48" xlink:to="loc_us-gaap_StatementClassOfStockAxis_01a17520-7f6b-7264-a222-1454ba6a1d08" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a17520-7f6b-7264-a222-1454ba6a1d08_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a17520-7f6b-7264-a222-1454ba6a1d08" xlink:to="loc_us-gaap_ClassOfStockDomain_01a17520-7f6b-7264-a222-1454ba6a1d08_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a17520-7f6b-7e14-b624-378b5ede3115" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a17520-7f6b-7264-a222-1454ba6a1d08" xlink:to="loc_us-gaap_ClassOfStockDomain_01a17520-7f6b-7e14-b624-378b5ede3115" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_RedeemablePreferredNoncontrollingInterestMember_01a17520-7f6b-7012-b01e-861f32c04516" xlink:href="wdq-20260930.xsd#wdq_RedeemablePreferredNoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a17520-7f6b-7e14-b624-378b5ede3115" xlink:to="loc_wdq_RedeemablePreferredNoncontrollingInterestMember_01a17520-7f6b-7012-b01e-861f32c04516" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_SeriesA1PreferredStockMember_01a17520-7f6b-7c2c-ad29-717b4917b558" xlink:href="wdq-20260930.xsd#wdq_SeriesA1PreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_RedeemablePreferredNoncontrollingInterestMember_01a17520-7f6b-7012-b01e-861f32c04516" xlink:to="loc_wdq_SeriesA1PreferredStockMember_01a17520-7f6b-7c2c-ad29-717b4917b558" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_01a17520-7f6b-7ea3-8e65-30ecba857e37" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_RedeemablePreferredNoncontrollingInterestMember_01a17520-7f6b-7012-b01e-861f32c04516" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_01a17520-7f6b-7ea3-8e65-30ecba857e37" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_IncreaseDecreaseInTemporaryEquityUnitsRollForward_01a17520-7f6b-7885-9129-dcb6199f9929" xlink:href="wdq-20260930.xsd#wdq_IncreaseDecreaseInTemporaryEquityUnitsRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-73fe-ba43-fe82040c60fc" xlink:to="loc_wdq_IncreaseDecreaseInTemporaryEquityUnitsRollForward_01a17520-7f6b-7885-9129-dcb6199f9929" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_01a17520-7f6b-7619-b4b6-b7ca627b8407" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_IncreaseDecreaseInTemporaryEquityUnitsRollForward_01a17520-7f6b-7885-9129-dcb6199f9929" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_01a17520-7f6b-7619-b4b6-b7ca627b8407" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_TemporaryEquitySharesIssuanceOfPreferredUnitsNetOfIssuanceCostsAndFairValueOfWarrant_01a17520-7f6b-7908-b875-5ed8afb9d345" xlink:href="wdq-20260930.xsd#wdq_TemporaryEquitySharesIssuanceOfPreferredUnitsNetOfIssuanceCostsAndFairValueOfWarrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_IncreaseDecreaseInTemporaryEquityUnitsRollForward_01a17520-7f6b-7885-9129-dcb6199f9929" xlink:to="loc_wdq_TemporaryEquitySharesIssuanceOfPreferredUnitsNetOfIssuanceCostsAndFairValueOfWarrant_01a17520-7f6b-7908-b875-5ed8afb9d345" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_TemporaryEquitySharesRedemptionOfPreferredUnits_01a17520-7f6b-76c2-8b76-694919d76ad3" xlink:href="wdq-20260930.xsd#wdq_TemporaryEquitySharesRedemptionOfPreferredUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_IncreaseDecreaseInTemporaryEquityUnitsRollForward_01a17520-7f6b-7885-9129-dcb6199f9929" xlink:to="loc_wdq_TemporaryEquitySharesRedemptionOfPreferredUnits_01a17520-7f6b-76c2-8b76-694919d76ad3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_01a17520-7f6b-7309-83dd-66dc52a99271" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_IncreaseDecreaseInTemporaryEquityAmountRollForward_01a17520-7f6b-7eae-8543-69f3d2e6b773" xlink:href="wdq-20260930.xsd#wdq_IncreaseDecreaseInTemporaryEquityAmountRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredUnitsLineItems_01a17520-7f6b-73fe-ba43-fe82040c60fc" xlink:to="loc_wdq_IncreaseDecreaseInTemporaryEquityAmountRollForward_01a17520-7f6b-7eae-8543-69f3d2e6b773" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_01a17520-7f6b-722b-8515-e90000142025" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_IncreaseDecreaseInTemporaryEquityAmountRollForward_01a17520-7f6b-7eae-8543-69f3d2e6b773" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_01a17520-7f6b-722b-8515-e90000142025" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_TemporaryEquityValueIssuanceOfPreferredUnitsNetOfIssuanceCostsAndFairValueOfWarrant_01a17520-7f6b-7fb6-88e0-09c9013075d0" xlink:href="wdq-20260930.xsd#wdq_TemporaryEquityValueIssuanceOfPreferredUnitsNetOfIssuanceCostsAndFairValueOfWarrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_IncreaseDecreaseInTemporaryEquityAmountRollForward_01a17520-7f6b-7eae-8543-69f3d2e6b773" xlink:to="loc_wdq_TemporaryEquityValueIssuanceOfPreferredUnitsNetOfIssuanceCostsAndFairValueOfWarrant_01a17520-7f6b-7fb6-88e0-09c9013075d0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_TemporaryEquityValueRedemptionOfPreferredUnits_01a17520-7f6b-7b83-8c92-413fb35a0807" xlink:href="wdq-20260930.xsd#wdq_TemporaryEquityValueRedemptionOfPreferredUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_IncreaseDecreaseInTemporaryEquityAmountRollForward_01a17520-7f6b-7eae-8543-69f3d2e6b773" xlink:to="loc_wdq_TemporaryEquityValueRedemptionOfPreferredUnits_01a17520-7f6b-7b83-8c92-413fb35a0807" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_TemporaryEquityAccretionOfDividendsAttributableToParent_01a17520-7f6b-7be3-b693-53950a12af7c" xlink:href="wdq-20260930.xsd#wdq_TemporaryEquityAccretionOfDividendsAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_IncreaseDecreaseInTemporaryEquityAmountRollForward_01a17520-7f6b-7eae-8543-69f3d2e6b773" xlink:to="loc_wdq_TemporaryEquityAccretionOfDividendsAttributableToParent_01a17520-7f6b-7be3-b693-53950a12af7c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_TemporaryEquityAccretionOfDividendsAttributableToCommonStockholdersBasic_01a17520-7f6b-77a7-a0f0-3ef0b4d1257e" xlink:href="wdq-20260930.xsd#wdq_TemporaryEquityAccretionOfDividendsAttributableToCommonStockholdersBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_IncreaseDecreaseInTemporaryEquityAmountRollForward_01a17520-7f6b-7eae-8543-69f3d2e6b773" xlink:to="loc_wdq_TemporaryEquityAccretionOfDividendsAttributableToCommonStockholdersBasic_01a17520-7f6b-77a7-a0f0-3ef0b4d1257e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_TemporaryEquityIncreaseFromDividendDistribution_01a17520-7f6b-7c5c-9a1d-e9d329018407" xlink:href="wdq-20260930.xsd#wdq_TemporaryEquityIncreaseFromDividendDistribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_IncreaseDecreaseInTemporaryEquityAmountRollForward_01a17520-7f6b-7eae-8543-69f3d2e6b773" xlink:to="loc_wdq_TemporaryEquityIncreaseFromDividendDistribution_01a17520-7f6b-7c5c-9a1d-e9d329018407" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment_01a17520-7f6b-770f-970e-79f5555f9d70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wdq_IncreaseDecreaseInTemporaryEquityAmountRollForward_01a17520-7f6b-7eae-8543-69f3d2e6b773" xlink:to="loc_us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment_01a17520-7f6b-770f-970e-79f5555f9d70" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_01a17520-7f6b-7034-a26f-4156ac0aea90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/NETLOSSPERSHARENarrativeDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#NETLOSSPERSHARENarrativeDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/NETLOSSPERSHARENarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightLineItems_01a17520-7f6b-7757-9d01-38224c743a2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightTable_01a17520-7f6b-7e15-9f8f-3d1435983c39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_01a17520-7f6b-7757-9d01-38224c743a2e" xlink:to="loc_us-gaap_ClassOfWarrantOrRightTable_01a17520-7f6b-7e15-9f8f-3d1435983c39" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a17520-7f6b-7b9f-85c6-d884032208a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_01a17520-7f6b-7e15-9f8f-3d1435983c39" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a17520-7f6b-7b9f-85c6-d884032208a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a17520-7f6b-7b9f-85c6-d884032208a2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a17520-7f6b-7b9f-85c6-d884032208a2" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a17520-7f6b-7b9f-85c6-d884032208a2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a17520-7f6b-7640-8fbd-fb5f12bf8c53" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a17520-7f6b-7b9f-85c6-d884032208a2" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a17520-7f6b-7640-8fbd-fb5f12bf8c53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_01a17520-7f6b-7d23-aec0-88a6c3179274" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a17520-7f6b-7640-8fbd-fb5f12bf8c53" xlink:to="loc_us-gaap_TreasuryStockCommonMember_01a17520-7f6b-7d23-aec0-88a6c3179274" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_01a17520-7f6b-736a-8eac-f00a816034df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_01a17520-7f6b-7e15-9f8f-3d1435983c39" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_01a17520-7f6b-736a-8eac-f00a816034df" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a17520-7f6b-736a-8eac-f00a816034df_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a17520-7f6b-736a-8eac-f00a816034df" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a17520-7f6b-736a-8eac-f00a816034df_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a17520-7f6b-7de1-8d43-4e3da52daf45" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a17520-7f6b-736a-8eac-f00a816034df" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a17520-7f6b-7de1-8d43-4e3da52daf45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_EarnoutTargetMember_01a17520-7f6b-7946-9c11-edefb0a6df49" xlink:href="wdq-20260930.xsd#wdq_EarnoutTargetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a17520-7f6b-7de1-8d43-4e3da52daf45" xlink:to="loc_wdq_EarnoutTargetMember_01a17520-7f6b-7946-9c11-edefb0a6df49" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_01a17520-7f6b-7edc-bfd4-e82c105043b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_01a17520-7f6b-7757-9d01-38224c743a2e" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_01a17520-7f6b-7edc-bfd4-e82c105043b6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/NETLOSSPERSHAREAntidilutiveSecuritiesExcludedfromComputationofEarningsPerShareDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#NETLOSSPERSHAREAntidilutiveSecuritiesExcludedfromComputationofEarningsPerShareDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/NETLOSSPERSHAREAntidilutiveSecuritiesExcludedfromComputationofEarningsPerShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a17520-7f6b-79a6-83bf-03dc2a08dc78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_01a17520-7f6b-72e7-8287-192e34c9c505" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a17520-7f6b-79a6-83bf-03dc2a08dc78" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_01a17520-7f6b-72e7-8287-192e34c9c505" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a17520-7f6b-73e3-8110-9a64b14c1b7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_01a17520-7f6b-72e7-8287-192e34c9c505" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a17520-7f6b-73e3-8110-9a64b14c1b7c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a17520-7f6b-73e3-8110-9a64b14c1b7c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a17520-7f6b-73e3-8110-9a64b14c1b7c" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a17520-7f6b-73e3-8110-9a64b14c1b7c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a17520-7f6b-768a-8a87-5a8ef500c298" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a17520-7f6b-73e3-8110-9a64b14c1b7c" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a17520-7f6b-768a-8a87-5a8ef500c298" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_01a17520-7f6b-7836-bcfd-a553b14e54e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a17520-7f6b-768a-8a87-5a8ef500c298" xlink:to="loc_us-gaap_EmployeeStockOptionMember_01a17520-7f6b-7836-bcfd-a553b14e54e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_01a17520-7f6b-78b2-8d95-83f1a028e73d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a17520-7f6b-768a-8a87-5a8ef500c298" xlink:to="loc_us-gaap_PerformanceSharesMember_01a17520-7f6b-78b2-8d95-83f1a028e73d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_01a17520-7f6b-7f3f-a83e-71f5e18056c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a17520-7f6b-768a-8a87-5a8ef500c298" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_01a17520-7f6b-7f3f-a83e-71f5e18056c7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_01a17520-7f6b-7ee0-8f03-25d4b4c13379" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a17520-7f6b-768a-8a87-5a8ef500c298" xlink:to="loc_us-gaap_WarrantMember_01a17520-7f6b-7ee0-8f03-25d4b4c13379" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_01a17520-7f6b-74a0-92bc-e453017a25e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a17520-7f6b-768a-8a87-5a8ef500c298" xlink:to="loc_us-gaap_CommonClassBMember_01a17520-7f6b-74a0-92bc-e453017a25e4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_ContingentWarrantsMember_01a17520-7f6b-71b7-9fee-f54504a45098" xlink:href="wdq-20260930.xsd#wdq_ContingentWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a17520-7f6b-768a-8a87-5a8ef500c298" xlink:to="loc_wdq_ContingentWarrantsMember_01a17520-7f6b-71b7-9fee-f54504a45098" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_01a17520-7f6b-7e49-9c29-971781befc8b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a17520-7f6b-79a6-83bf-03dc2a08dc78" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_01a17520-7f6b-7e49-9c29-971781befc8b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/STOCKBASEDCOMPENSATIONNarrativeDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#STOCKBASEDCOMPENSATIONNarrativeDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/STOCKBASEDCOMPENSATIONNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a17520-7f6b-74d0-bffc-d579720696e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a17520-7f6b-7513-8844-8803b5e17f40" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a17520-7f6b-74d0-bffc-d579720696e0" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a17520-7f6b-7513-8844-8803b5e17f40" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_01a17520-7f6b-726d-937c-0afdcc9d8d68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a17520-7f6b-7513-8844-8803b5e17f40" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_01a17520-7f6b-726d-937c-0afdcc9d8d68" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a17520-7f6b-726d-937c-0afdcc9d8d68_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_01a17520-7f6b-726d-937c-0afdcc9d8d68" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a17520-7f6b-726d-937c-0afdcc9d8d68_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a17520-7f6b-759f-9060-0d214802b9a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_01a17520-7f6b-726d-937c-0afdcc9d8d68" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a17520-7f6b-759f-9060-0d214802b9a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_A2022OmnibusEquityIncentivePlan2022PlanMember_01a17520-7f6b-76a0-973a-2ef0dac06bfd" xlink:href="wdq-20260930.xsd#wdq_A2022OmnibusEquityIncentivePlan2022PlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a17520-7f6b-759f-9060-0d214802b9a3" xlink:to="loc_wdq_A2022OmnibusEquityIncentivePlan2022PlanMember_01a17520-7f6b-76a0-973a-2ef0dac06bfd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_01a17520-7f6b-7aa2-b2db-ea19f883aa96" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a17520-7f6b-74d0-bffc-d579720696e0" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_01a17520-7f6b-7aa2-b2db-ea19f883aa96" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/STOCKBASEDCOMPENSATIONStockbasedCompensationExpenseDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#STOCKBASEDCOMPENSATIONStockbasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/STOCKBASEDCOMPENSATIONStockbasedCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a17520-7f6b-7623-99f1-484eda7f7395" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a17520-7f6b-7c4e-aa27-264a2c9db98b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a17520-7f6b-7623-99f1-484eda7f7395" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a17520-7f6b-7c4e-aa27-264a2c9db98b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_01a17520-7f6b-76ee-afc8-159cc43212f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a17520-7f6b-7c4e-aa27-264a2c9db98b" xlink:to="loc_us-gaap_PlanNameAxis_01a17520-7f6b-76ee-afc8-159cc43212f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_01a17520-7f6b-76ee-afc8-159cc43212f8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_01a17520-7f6b-76ee-afc8-159cc43212f8" xlink:to="loc_us-gaap_PlanNameDomain_01a17520-7f6b-76ee-afc8-159cc43212f8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_01a17520-7f6b-7dfc-ac55-7f1813ae9687" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_01a17520-7f6b-76ee-afc8-159cc43212f8" xlink:to="loc_us-gaap_PlanNameDomain_01a17520-7f6b-7dfc-ac55-7f1813ae9687" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_A2022OmnibusEquityIncentivePlan2022PlanMember_01a17520-7f6b-7eb8-814b-98246b4f13b6" xlink:href="wdq-20260930.xsd#wdq_A2022OmnibusEquityIncentivePlan2022PlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_01a17520-7f6b-7dfc-ac55-7f1813ae9687" xlink:to="loc_wdq_A2022OmnibusEquityIncentivePlan2022PlanMember_01a17520-7f6b-7eb8-814b-98246b4f13b6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_ParentEquityAwardsMember_01a17520-7f6b-79e4-8b42-5329878f8123" xlink:href="wdq-20260930.xsd#wdq_ParentEquityAwardsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_01a17520-7f6b-7dfc-ac55-7f1813ae9687" xlink:to="loc_wdq_ParentEquityAwardsMember_01a17520-7f6b-79e4-8b42-5329878f8123" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a17520-7f6b-760b-80c7-67610df2744c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a17520-7f6b-7623-99f1-484eda7f7395" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a17520-7f6b-760b-80c7-67610df2744c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://opalfuels.com/role/COMMITMENTSANDCONTINGENCIESNarrativeDetails" xlink:type="simple" xlink:href="wdq-20260930.xsd#COMMITMENTSANDCONTINGENCIESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://opalfuels.com/role/COMMITMENTSANDCONTINGENCIESNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_01a17520-7f6b-7d6a-84f8-bb7ef6ac0b37" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_01a17520-7f6b-7549-9fba-90a2d0dd3f30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a17520-7f6b-7d6a-84f8-bb7ef6ac0b37" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_01a17520-7f6b-7549-9fba-90a2d0dd3f30" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_01a17520-7f6b-7412-900d-7fab1ed4afc0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_01a17520-7f6b-7549-9fba-90a2d0dd3f30" xlink:to="loc_us-gaap_CreditFacilityAxis_01a17520-7f6b-7412-900d-7fab1ed4afc0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a17520-7f6b-7412-900d-7fab1ed4afc0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_01a17520-7f6b-7412-900d-7fab1ed4afc0" xlink:to="loc_us-gaap_CreditFacilityDomain_01a17520-7f6b-7412-900d-7fab1ed4afc0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a17520-7f6b-76be-be63-00417ede22b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_01a17520-7f6b-7412-900d-7fab1ed4afc0" xlink:to="loc_us-gaap_CreditFacilityDomain_01a17520-7f6b-76be-be63-00417ede22b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StandbyLettersOfCreditMember_01a17520-7f6b-7c18-acd1-6439181058c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StandbyLettersOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_01a17520-7f6b-76be-be63-00417ede22b1" xlink:to="loc_us-gaap_StandbyLettersOfCreditMember_01a17520-7f6b-7c18-acd1-6439181058c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a17520-7f6b-76ee-a7f8-33ad2b9130c1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_01a17520-7f6b-7549-9fba-90a2d0dd3f30" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a17520-7f6b-76ee-a7f8-33ad2b9130c1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_01a17520-7f6b-76ee-a7f8-33ad2b9130c1_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a17520-7f6b-76ee-a7f8-33ad2b9130c1" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_01a17520-7f6b-76ee-a7f8-33ad2b9130c1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_01a17520-7f6b-7464-88fb-c5c5998523f2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a17520-7f6b-76ee-a7f8-33ad2b9130c1" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_01a17520-7f6b-7464-88fb-c5c5998523f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_Land2GasLLCMember_01a17520-7f6b-75e3-b7bf-ef330d90f134" xlink:href="wdq-20260930.xsd#wdq_Land2GasLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_01a17520-7f6b-7464-88fb-c5c5998523f2" xlink:to="loc_wdq_Land2GasLLCMember_01a17520-7f6b-75e3-b7bf-ef330d90f134" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_01a17520-7f6b-76ad-93bd-d3cd44d28b3f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_01a17520-7f6b-7549-9fba-90a2d0dd3f30" xlink:to="loc_srt_CounterpartyNameAxis_01a17520-7f6b-76ad-93bd-d3cd44d28b3f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17520-7f6b-76ad-93bd-d3cd44d28b3f_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_01a17520-7f6b-76ad-93bd-d3cd44d28b3f" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17520-7f6b-76ad-93bd-d3cd44d28b3f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17520-7f6b-727d-a622-557913cf8194" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_01a17520-7f6b-76ad-93bd-d3cd44d28b3f" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17520-7f6b-727d-a622-557913cf8194" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_AtheneAnnuityAndLifeCompanyAndAtheneAnnuityReIILtd.Member_01a17520-7f6b-750e-8b3d-9f0ec64605b3" xlink:href="wdq-20260930.xsd#wdq_AtheneAnnuityAndLifeCompanyAndAtheneAnnuityReIILtd.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17520-7f6b-727d-a622-557913cf8194" xlink:to="loc_wdq_AtheneAnnuityAndLifeCompanyAndAtheneAnnuityReIILtd.Member_01a17520-7f6b-750e-8b3d-9f0ec64605b3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_VECPartnersIncDbaCEIBuildersCEIMember_01a17520-7f6b-79ff-9055-4737fd7cf0e0" xlink:href="wdq-20260930.xsd#wdq_VECPartnersIncDbaCEIBuildersCEIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17520-7f6b-727d-a622-557913cf8194" xlink:to="loc_wdq_VECPartnersIncDbaCEIBuildersCEIMember_01a17520-7f6b-79ff-9055-4737fd7cf0e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_01a17520-7f6b-7ba4-861e-735f9ef0869b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_01a17520-7f6b-7549-9fba-90a2d0dd3f30" xlink:to="loc_dei_LegalEntityAxis_01a17520-7f6b-7ba4-861e-735f9ef0869b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a17520-7f6b-7ba4-861e-735f9ef0869b_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_01a17520-7f6b-7ba4-861e-735f9ef0869b" xlink:to="loc_dei_EntityDomain_01a17520-7f6b-7ba4-861e-735f9ef0869b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a17520-7f6b-7891-aa81-402b3cc6f80d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_01a17520-7f6b-7ba4-861e-735f9ef0869b" xlink:to="loc_dei_EntityDomain_01a17520-7f6b-7891-aa81-402b3cc6f80d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_Land2GasLLCMember_01a17520-7f6b-715b-8e65-0f3e918f6f77" xlink:href="wdq-20260930.xsd#wdq_Land2GasLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01a17520-7f6b-7891-aa81-402b3cc6f80d" xlink:to="loc_wdq_Land2GasLLCMember_01a17520-7f6b-715b-8e65-0f3e918f6f77" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_MDDigesterLLCMember_01a17520-7f6b-760d-840a-5bf15d674f22" xlink:href="wdq-20260930.xsd#wdq_MDDigesterLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01a17520-7f6b-7891-aa81-402b3cc6f80d" xlink:to="loc_wdq_MDDigesterLLCMember_01a17520-7f6b-760d-840a-5bf15d674f22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_01a17520-7f6b-7cd7-9a9f-6bc4fbee5353" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a17520-7f6b-7d6a-84f8-bb7ef6ac0b37" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_01a17520-7f6b-7cd7-9a9f-6bc4fbee5353" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLongTermLinesOfCredit_01a17520-7f6b-73e4-9004-1ef2f914a7b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromLongTermLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a17520-7f6b-7d6a-84f8-bb7ef6ac0b37" xlink:to="loc_us-gaap_ProceedsFromLongTermLinesOfCredit_01a17520-7f6b-73e4-9004-1ef2f914a7b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_01a17520-7f6b-753c-be2b-8c848edabed6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a17520-7f6b-7d6a-84f8-bb7ef6ac0b37" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_01a17520-7f6b-753c-be2b-8c848edabed6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_InvestmentTaxCreditPurchaseAgreement_01a17520-7f6b-7a3e-a557-8d53dde58474" xlink:href="wdq-20260930.xsd#wdq_InvestmentTaxCreditPurchaseAgreement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a17520-7f6b-7d6a-84f8-bb7ef6ac0b37" xlink:to="loc_wdq_InvestmentTaxCreditPurchaseAgreement_01a17520-7f6b-7a3e-a557-8d53dde58474" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_ProceedsFromInvestmentTaxCredit_01a17520-7f6b-7b09-869c-2c5eb0c5691e" xlink:href="wdq-20260930.xsd#wdq_ProceedsFromInvestmentTaxCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a17520-7f6b-7d6a-84f8-bb7ef6ac0b37" xlink:to="loc_wdq_ProceedsFromInvestmentTaxCredit_01a17520-7f6b-7b09-869c-2c5eb0c5691e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_GuarantorObligationsMaximumExposurePercent_01a17520-7f6b-7f54-bc2c-d6f653d6d70a" xlink:href="wdq-20260930.xsd#wdq_GuarantorObligationsMaximumExposurePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a17520-7f6b-7d6a-84f8-bb7ef6ac0b37" xlink:to="loc_wdq_GuarantorObligationsMaximumExposurePercent_01a17520-7f6b-7f54-bc2c-d6f653d6d70a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_LossContingencyEstimateOfPossibleLossPerContract_01a17520-7f6b-7d8d-985b-5c454a71095d" xlink:href="wdq-20260930.xsd#wdq_LossContingencyEstimateOfPossibleLossPerContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a17520-7f6b-7d6a-84f8-bb7ef6ac0b37" xlink:to="loc_wdq_LossContingencyEstimateOfPossibleLossPerContract_01a17520-7f6b-7d8d-985b-5c454a71095d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_01a17520-7f6b-7179-807a-ecd7f31a3143" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingencyEstimateOfPossibleLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a17520-7f6b-7d6a-84f8-bb7ef6ac0b37" xlink:to="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_01a17520-7f6b-7179-807a-ecd7f31a3143" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_wdq_LossContingencyEstimateOfPossibleLossSubcontractors_01a17520-7f6b-797d-8087-1cfa81dc3339" xlink:href="wdq-20260930.xsd#wdq_LossContingencyEstimateOfPossibleLossSubcontractors"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_01a17520-7f6b-7d6a-84f8-bb7ef6ac0b37" xlink:to="loc_wdq_LossContingencyEstimateOfPossibleLossSubcontractors_01a17520-7f6b-797d-8087-1cfa81dc3339" xlink:type="arc" order="8"/>
  </link:definitionLink>
</link:linkbase>
