This study investigates the characteristics of transport phenomena in the cathode gas diffusion layer (GDL) of a proton exchange membrane fuel cell (PEMFC) and their influences on cell performance by utilizing a two-phase flow model based on a multiphase mixture formulation. The profiles of liquid water saturation and oxygen concentration across the GDL are obtained by a direct numerical procedure, and the corresponding polarization curves are determined as well. The results show that the liquid water generated by the electrochemical reaction could significantly reduce the effective porosity of the GDL under high current density conditions to hinder oxygen transport through the GDL. The removal rate of liquid water due to capillarity-induced motion can be enhanced conspicuously by an increase in hydrophobicity at first, and this effect then diminishes gradually. The effects of porosity and thickness of the GDL, inlet velocity of reactant gas, and gas channel length on the cell performance are also examined in detail. The results provide insights into the transport mechanisms in the GDL and benefit the design of PEMFCs. (c) 2006 Elsevier B.V. All rights reserved.