This paper describes a two-phase, one-dimensional steady-state, isothermal model of a fuel cell region consisting of the catalyst and gas diffusion layers bonded to a proton exchange membrane (PEM). A thin film-agglomerate approach is used to model the catalyst layer. The effect of water flooding in the gas diffusion layer and catalyst layer of the cathode on the overall cell performance was investigated. The simulation results confirmed that the water-flooding situation in the catalyst layer is more severe than that in the backing layer since water is first produced in the catalyst layer. The catalyst layer should be considered as an individual domain. The effect of operating parameters that affect the water generation and removal process, such as the inlet relative humidity of the cathode and anode streams and operating temperature was studied. The results show good agreement with the experimental observations. (C) 2004 The Electrochemical Society.