The proton exchange membrane fuel cell performance of carbon-supported Pt, PtRu, and PtMo catalysts on reformate gas mixtures was investigated. The catalysts were tested as low Pt loaded electrodes in membrane electrode assemblies at 80degreesC using H-2; 10, 40, 100 ppm CO in H-2: 25% CO2 in H-2, and 40 ppm CO/25% CO2 in H-2 reformate gas mixtures as the fuel stream, The PtMo catalyst showed better CO tolerance than the PtRu catalyst at 100 ppm, but showed poorer CO2 tolerance to both Pt and PtRu. With 40 ppm CO/25% CO2 in H-2, PtMo showed inferior overall reformate tolerance to PtRu.