In the present study, the results of the numerical implementation of a mathematical model of a planar, anode-supported SOFC are reported. The mathematical model is solved in a 3D environment, and is validated by comparison with three different polarization curves, obtained at different operating conditions. The results show the importance of some tridimensional phenomena and their effect on the fuel cell performance. In particular, in-plane diffusion within the electrodes and non-uniform gas distribution within the gas channels are identified and analyzed. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.