A two-dimensional, single phase, multi-component model is developed to study the effects of cathode catalyst layer thickness on DMFC's performance. The simulations consider the effects of mixed potentials as well as the distribution of methanol concentration in the cathode catalyst layer, normally neglected by most DMFC models. In other words, the assumption of zero methanol concentration at the interface between the membrane and cathode catalyst layer (CCL) is not used in this model. COMSOL Multiphysics V4.3, a finite element analysis solver and simulation software, is employed to solve the fully coupled set of equations for electrochemical kinetics, continuity, momentum and species. There is a good agreement between the modeling results and the experimental data. Further modeling results show that neglecting methanol contamination in the CCL, i.e. assuming that methanol concentration goes to zero at the membrane/cathode interface, significantly overpredicts the fuel cell performance. (C) 2013 Elsevier B.V. All rights reserved.