Field campaigns in the summers of 2010, 2019, and 2023 measured methane (CH4), carbon dioxide (CO2), carbon monoxide (CO), and C2–C5 alkanes throughout the Los Angeles (LA) Basin aboard the NASA DC-8 and NOAA P-3 aircraft. California (CA) legislation currently requires that greenhouse gas emissions be reduced to 40% below 1990 levels by 2030, which will require knowing the sources of urban methane emissions to achieve this goal. Examining the relative emission ratios of these various alkanes and CH4 versus CO provides valuable insight into the CH4 contributions of different sources in the LA Basin. This analysis shows that the relative emissions of CH4 to on- and off-road combustion sources has increased since 2010 in the LA Basin. Further, using CA Air Resources Board CO emissions alongside CH4/ CO enhancement ratios, we determine summertime CH4 emissions from the LA Basin. This analysis shows how CH4 sources have changed in the past 13 years, providing insight into how CA is performing on their greenhouse gas reduction goals.