The objective of this work is to examine the effects of the flow channel area ratio (40%, 50%, and 60%) on the reactant gas transport and the cell performance of proton exchange membrane fuel cells (PEMFCs) with parallel and interdigitated flow channel designs. The effects of liquid water formation on the reactant gas transport are taken into account in the present study. Higher flow area ratios are expected to provide more area for fuel diffusion into the gas diffusion layer to enhance the electrochemical reaction rate and improve cell performance. Numerical predictions show that the cell performance for parallel flow channel design can be enhanced by increasing the flow channel area ratio and the best overall cell performance occurs for a flow channel area ratio of 60%. For the interdigitated flow channel design, because the fuel transport is by forced convection rather than diffusion, the flow channel area ratio has less effect on cell performance. Taking into account liquid water removal and pressure losses, the optimal cell performance occurs for a flow channel area ratio of 50% for the interdigitated flow channel design. The results also show that the flow channel area ratio and liquid water distribution significantly influence cell performance at lower voltages. (c) 2007 The Electrochemical Society.