Semi-analytical quasi-2D (Q2D) model of a PEFC is modified for the case of constant oxygen stoichiometry. The limits of validity of approximation of ideal membrane humidification are established. Q2D and numerical quasi-3D models are compared. Variation of just one parameter enables superimpose the polarization curves obtained from the two models. The profiles of local current density resulting from the two models then differ only by 5%. This suggests, that local 3D effects due to rib/channel alternation can be effectively accounted for within the scope of along-the-channel Q2D model by variation of a single parameter. Copyright (c) 2005 John Wiley & Sons, Ltd.