The objective of this work is to study a high-temperature proton exchange membrane fuel cell using CO- and methane-containing hydrogen-rich gases because of the advantages of high operating temperature and the growing feasibility of using natural gases or methane as the sources of hydrogen-rich reformate gases. According to the experimental results, it is suggested that the fuel cell be operated at 180 A degrees C under reformate gases with high CO concentrations to avoid not only a significant decrease in performance, but also severe potential oscillations. In addition, the anode oxidation reaction is more sensitive to the temperature than the cathode reduction reaction under CO-containing H-2. On the other hand, the effects of methane in the reformate gas on the fuel cell can be ignored because the existence of methane causes neither a decrease in the cell performance nor an increase in the anodic charge transfer resistance. Thus, the CO concentration and operating temperature are still the two dominant parameters with regard to the cell performance under CO- and methane-containing hydrogen-rich gases. [GRAPHICS] .