We estimate the overall CO 2 , CH 4 , and CO flux from the South Coast Air Basin using an inversion that couples Total Carbon Column Observing Network (TCCON) and Orbiting Carbon Observatory-2 (OCO-2) observations, with the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model, and the Open-source Data Inventory for Anthropogenic CO 2 (ODIAC). Using TCCON data we estimate the direct net CO 2 flux from the SoCAB to be 139 ± 35 Tg CO 2 yr −1 for the study period of July 2013–August 2016. We obtain a slightly lower estimate of 118 ± 29 Tg CO 2 yr −1 using OCO-2 data. These CO 2 emission estimates are in general agreement with previous work. Our net CH 4 (325 ± 81 Gg CH 4 yr −1 ) flux estimate is slightly lower than central values from previous top-down studies going back to 2010 (342–440 Gg CH 4 yr −1 ). CO emissions are estimated at 555 ± 136 Gg CO yr −1 , much lower than previous top-down estimates (1440 Gg CO yr −1 ). Given the decreasing emissions of CO, this finding is not unexpected. We perform sensitivity tests to estimate how much errors in the prior, errors in the covariance, different inversions schemes or a coarser dynamical model influence the emission estimates. Overall, the uncertainty is estimated to be 25 %, with the largest contribution from the dynamical model. The methods described are scalable and can be used to estimate direct net CO 2 fluxes from other urban regions.