Mathematical modeling is a powerful tool for improving the performance of fuel-cell stacks. In the present work, a mathematical model has been developed to study the performance of a proton exchange membrane fuel cell (PEMFC) at different operation variables. The effects of different operating para-meters on the performance of PEMFC have been studied using pure hydrogen on the anode side and air on the cathode side. Results with different fuel-cell operating temperatures, different operating pressures and various combinations of these parameters have been obtained. The possible mechanisms of the parameter effects and their inter-relationships are discussed. The modeling results compare well with the available experimental results. The comparison shows good agreement between the modeling results and the experimental data.