A detailed steady-state isothermal two-dimensional model of a proton exchange membrane fuel cell has been developed. A finite element method was used to solve this multi-component transport model coupled with flow in porous medium, charge balance, electrochemical kinetics, and a rigorous water balance in the membrane. The model-predicted fuel cell performance curves are compared with published experimental results and a good agreement was found. The complex water balance in the membrane was investigated and the operating conditions where the membrane becomes dehydrated were identified. The effects of channel width and bipolar plate shoulder dimensions, porosity, and the relative humidity of the inlet streams on the fuel cell performance are evaluated. It was found that smaller width channels and bipolar plate shoulders were required for high current density operations. As the electrode area under the bipolar plate shoulder increases, the fuel cell benefits more from higher porosity electrodes. The anode gas stream's relative humidity was found to be more critical for fuel cell performance than the cathode gas relative humidity. (c) 2005 Elsevier B.V. All rights reserved.