Adequate reactant gas distribution and water management are critical parameters for a fuel cell stack to perform properly and avoid certain failure modes. In this study, an approach is used in which the cathode flow field active area is changed with changing operating conditions. This approach maintains high and stable performance in the fuel cell system without significantly increasing the parasitic load. Such a dynamic flow field is particularly beneficial for applications with a wide range of operating conditions. (c) 2007 The Electrochemical Society.