The effect of copper compounds and phosphorus-molybdenum-vanadium heteropoly acids (HPAs) H5PMo10V2O40 and H7PMo8V4O40 used as cocatalysts in the cooxidation of propane and CO in the presence of rhodium, palladium, and platinum compounds in an aqueous AcOH medium has been studied. It has been shown that these HPAs are fairly effective; however, in catalyst systems with rhodium and palladium compounds, these HPAs are inferior to Cu(I,II). The inner-sphere and outer-sphere reaction mechanisms have been studied as the most probable oxidation mechanisms; the contribution of each of the mechanisms to the overall process has been determined.