A three-dimensional, steady-state mathematical model is described to investigate the fluid flow, species transport and electrochemical reaction in the PEM fuel cells with conventional and interdigitated flow fields. The multidimensional characteristics of flow, species and current distributions are computed by method based on volume-control finite-discrete technique. After comparing the absolute value of convective and diffusion component of oxygen flux quantitatively, we found that forced convection transport mechanism is dominant for the interdigitated flow field design, however the diffusion transport is dominant for the conventional flow field design. The performance and the pressure loss of these two different designs are calculated and compared; results show that interdigitated flow field design have better performance for its advantage in mass-transport ability, however have larger pressure loss for its flow through the electrode. Finally, experimental results reported in the literature and predicted polarization curves are compared to evaluate the numerical model employed. (C) 2004 Elsevier B.V. All rights reserved.