Modeling of liquid water distribution in polymer electrolyte membrane fuel cells (PEMFCs) is challenged by uncertainties in characterizing the two-phase transport properties of the porous transport layer (PTL) and the catalyst layer (CL). Capillary pressure, representing both pore structures and wetting features of the porous media, is a key factor in controlling liquid water transport and distribution in the porous electrode of PEMFCs. By incorporating experimentally measured capillary pressure functions, a single-domain, three-dimensional, and two-phase transport model was developed to predict liquid water saturation in the PTL and CL of a PEMFC with long straight channels, where the two-phase flow complications were minimized at practical stoichiometry. In the cathode CL, the liquid water saturation was found to be higher under the channel than that under the ribs at high current densities. In the cathode PTL, however, the liquid water saturation level was observed to be lower under the channel than that under the ribs. At high current densities, the average water saturation levels are insensitive to current density and fall in the range of 0.4-0.5 in the CL and 0.2-0.3 in the PTL. Finally, the effects of liquid water on oxygen transport and cell performance were investigated. (c) 2007 The Electrochemical Society.