This study investigates the location of the gas-liquid interface under various humidity conditions in the cathode gas diffusion layer and the conventional flow field of a polymer electrolyte membrane fuel cell (PEMFC), using commercial computational fluid dynamics (CFDRC) analysis, based on a three-dimensional steady state isothermal model. The effects of the formation of liquid water on the transport of reactant gas are considered in the model. The simulation results indicate that the gas-liquid interface approaches the gas flow channel inlet and the cell performance declines gradually as liquid water obstructs the pores in the porous media as the relative humidity of the cathode is increased. Additionally, the oxygen fraction, the water fraction and the liquid water saturation field along the flow channel are presented. (c) 2006 Elsevier B.V. All rights reserved.