Computational fluid dynamics analysis was employed to investigate the performance of proton exchange membrane fuel cells (PEMFCs) with different channel geometries at high operating current densities. A 3D, non-isothermal model was used with a single straight channel geometry. Both anode and cathode humidifications were included in the model. In addition, phase transportation was included in the model to obtain the total water management for systems operating at different current densities. The simulation results showed that a rectangular channel cross-section gave higher cell voltages compared with trapezoidal and parallelogram channel cross-sections. However, the trapezoidal channel cross-section facilitated reactant diffusion, leading to more uniform reactant and local current density distributions over the reacting area, and thus to a lower cathode overpotential of the cell. Simulations of the three different channel cross-sections using the same boundary conditions showed that among the cell geometrical parameters, the shoulder width is one of the most influential in terms of its impact on cell performance. Simulations using different channel-shoulder width ratios showed that at high operating current densities, Ohmic losses significantly increase with decreasing shoulder width. In contrast, a smaller shoulder width facilitates the distribution of reactants and helps to reduce concentration losses. The simulations disclosed the existence of an optimum channel-shoulder width ratio that gives the highest cell voltage under high current density operating conditions. Under such conditions, however, the cell performance deteriorated dramatically with decreasing shoulder width, even when higher reactants flow rates and inlet velocities were used. (c) 2006 Elsevier B.V. All rights reserved.