We examine the electrocatalytic properties of a Pt/Vulcan carbon catalyst toward the electro-oxidation of CO and CO/H-2 mixtures under proton exchange membrane fuel cell (PEMFC) relevant conditions [60 to 80 degrees C, continuous reactant flow), employing rotating disk electrode (RDE) measurements. We demonstrate that our recently introduced thin-film RDE technique can he applied to predict the performance of real fuel cell anodes operating on CO-contaminated H-2. The method involves attaching the catalyst particles to a glassy carbon RDE via a thin Nafion film. The thin-film RDE technique opens the possibility for the mass-transport-free determination of the electrode kinetics at 100% catalyst utilization. At identical mass-specific current densities, the overpotentials for CO/H-2 oxidation measured with the thin-film RDE technique are in excellent agreement with performance data from PEMFC anodes. The kinetics of purl CO oxidation were investigated with CO/N-2, mixtures, revealing that the CO oxidation activity increases with decreasing CO partial pressure (negative reaction order). The observed ignition potential for CO oxidation was the same for both the CO/N-2 and the CO/H-2 mixtures. Two H-2 oxidation mechanisms in the presence of CO can be distinguished: (i) a high Tafel slope region at low overpotentials, where H-2 oxidation occurs in vacancies of the CO adlayer; and iii) a law Tafel slope region at high overpotentials where H-2 and CO oxidation occur simultaneously.