The performance of polymer electrolyte membrane (PEM) fuel cell stacks can be improved significantly by optimizing the design and operating conditions. In this study, performance modeling and optimization of a PEM fuel cell stack have been conducted. The pressure and molar flow rate distributions for the fuel and oxidant streams in the stack are determined with a flow network model incorporating the minor losses. The distributions are then used in the single cell model developed previously to evaluate the performance of PEM fuel cell stack. Analysis has been carried out for different fuel and oxidant flow configurations and bipolar plate designs. It was found that the minor losses increase the stack operating pressure and the power requirement for oxidant supply and alter the cell-to-cell voltage variations in the stack. A symmetric double inlet-single outlet topology provides optimal stack performance with reasonably low compressor power requirement for the reactant flow and minimum cell-to-cell voltage variations. The stack performance is considerably affected by the size and the number of flow channels on bipolar plate. Optimal stack performance requires the matching of the stack manifold designs, flow channels on the bipolar plates and the stack operating conditions. (c) 2005 Elsevier B.V. All rights reserved.