The gas transport in the porous electrode is treated by a phenomenological approach such that the gas concentration at the three-phase boundary (TPB) region is the additive superposition of that transported from the source, i.e. the gas channels. With plausible approximations and elemental algebra, analytical expressions are obtained to estimate the effects of ribs on the concentration polarization of planar fuel cell operations. It is shown that the model can closely reproduce the experimental concentration polarization curve for small and medium current density (up to about 2 A/cm(2)), providing a simple and effective method for engineering application. The concentration polarization caused by the presence of a rib is discussed and the concentration profiles with varying rib widths are illustrated. In connection with the electrical resistance, the determination of the optimal rib width for minimizing the overall polarization is also shown. (C) 2003 Elsevier Science B.V. All rights reserved.