A proton exchange membrane fuel cell (PEMFC) stack model which incorporates flow distribution effects and a reduced dimensional unit cell model is presented. The laws of Mass and Momentum Conservation are applied throughout the stack. Along the headers, flow splitting and recombination are applied at each tee junction, while along the unit cell channels, reactant consumption and byproduct production are accounted for. Cell performance is coupled to the channel conditions. Using this stack model, the sensitivity of stack performance to operating conditions (inlet velocity and pressure) and design parameters (manifold, flow configuration and friction factor) is investigated. In particular, performance under uniform, single anomaly, and random parameter distributions is investigated. (c) 2006 Elsevier B.V. All rights reserved.