AbstractSource attribution of natural gas emissions from fossil fuels in New Mexico's San Juan Basin (SJB) is challenging due to source heterogeneity and emissions transience. We demonstrate that ethane (C₂H₆) to methane (CH₄) mixing ratios can identify and separate sources over different scales using various measurement techniques. We report simultaneous CH₄ and C₂H₆ observations near a coal mine vent and oil and gas (O&G) emission sources using ground‐based in situ measurements in 2020/2021. During these campaigns, we observed a stable coal vent C₂H₆:CH₄ ratio of 1.28% ± 0.11%, discernibly different than nearby O&G source ratios ranging from 0.9% to 16.8%. We analyze airborne observations of the SJB taken in 2014/2015 that exhibit similar coal vent ratios and further show the region's heterogeneity. We identify episodic O&G sources, including a gas plant source detected in 2014/2015 that is absent in our 2020/2021 data. We examine total column observations of C₂H₆ and CH₄ made in 2013 with a solar spectrometer and find a C₂H₆:CH₄ ratio of 1.3% ± 0.4% for the coal vent. The stable and unique coal vent ratio relative to other O&G sources in the region is used to demonstrate that consistent attribution is possible using various measurement methods at multiple scales across many years. Finally, we demonstrate that using C₂H₆ as a proxy for fossil CH₄ inversions can inform detailed basin‐scale inversions, provided we understand source specific changes in the C₂H₆:CH₄ ratio like we report in the SJB.