We use aircraft observations of continental outflow over the western Pacific from the Transport and Chemical Evolution over the Pacific (TRACE-P) mission (March--April 2001), in combination with an optimal estimation inverse model, to improve emission estimates of carbon monoxide (CO) from Asia. A priori emissions and their errors are from a customized bottom-up Asian emission inventory for the TRACE-P period. The global three-dimensional GEOS-CHEM chemical transport model (CTM) is used as the forward model. The CTM transport error (20--30% of the CO concentration) is quantified from statistics of the difference between the aircraft observations of CO and the forward model results with a priori emissions, after removing the mean bias which is attributed to errors in the a priori emissions. Additional contributions to the error budget in the inverse analysis include the representation error (typically 5% of the CO concentration) and the measurement accuracy (≃2% of the CO concentration). We find that the inverse model can usefully constrain five sources: Chinese fuel consumption, Chinese biomass burning, total emissions from Korea and Japan, total emissions from Southeast Asia, and the ensemble of all other sources. The inversion indicates a 54% increase in anthropogenic emissions from China (to 168 Tg CO yr-1) relative to the a priori; this value is still much lower than had been derived in previous inversions using the CMDL network of surface observations. A posteriori emissions of biomass burning in Southeast Asia and China are much lower than a priori estimates.