The performance improvement of a proton exchange membrane fuel cell due to increased operating pressure must be balanced against the energy required to pressurize the reactant gases. This paper quantifies and assesses the effect of higher operating pressure on the net change in cell voltage at various operating temperatures, air stoichiometries, relative humidities, and humidity ratios. The analysis is performed to determine the power lost due to air compression at various operating current densities. The calculated results at high-pressure ratios demonstrate the significance of a higher operating temperature and a lower air stoichiometry on the net change in the cell voltage. Furthermore, better results are achieved at a humidity ratio of 0.10 than at 0.05 in terms of net change in the cell voltage, relative humidity, and stoichiometric ratio. (c) 2004 Elsevier B.V. All rights reserved.