The cell performance and transport phenomena in a proton exchange membrane fuel cell were analyzed numerically for cells with flow channels that are contracted at the outlet. The effects of various outlet contraction ratios and the liquid water production are examined in detail. The predicted results show that, for operating voltages higher than 0.7 V, the effect of the flow field design on the cell performance is not significant due to the weaker electrochemical reaction. However, for operating voltages lower than 0.7 V, the flow field design significantly affects the cell performance. The contracted channel design forces the reactants to flow into the gas diffusion layer and the catalyst layer, which enhances liquid water removal and increases reactant utilization, so the cell performance is improved compared with the conventional design. In addition, the cell performance increases with either decreasing the height contraction ratio or decreasing the length contraction ratio, with the decreasing length contraction ratio being preferred to the decreasing height contraction ratio due to the smaller pressure drops. (C) 2008 The Electrochemical Society.