Electrochemical oxidation of acetone, 2-propanol, and 1-propanol on Pt was studied by slow scan rate voltammetry at 170 °C using fuel cell with the membrane of the H3PO4 doped polybenzimidazole. Reaction rate orders with respect to partial pressures of the aliphatic compounds and water vapors were determined at E = 0.5 V and at E = 0.9 V, which correspond to low and high surface oxide coverages on Pt. At E = 0.5 V close to zero reaction rate orders in respect to vapor pressures of aliphatic reactants were found. At E = 0.5 V reaction, rate orders with respect to water vapor pressure were slightly higher than unity in all cases. At E = 0.9 V oxidation, reaction rate orders with respect to aliphatic reactant vapor pressure ranged within 0.6–1. Close to zero reaction rate orders with respect to water vapor pressure were found in all cases at E = 0.9 V.