Fuel cell flow channel scaling behavior has been investigated for three different flow pattern archetypes (interdigitated, serpentine, and spiral interdigitated) by employing computational fluid dynamics (CFD). The range of investigation covers flow channels of macro feature size (>500 mum) to micro feature size (<100 mum). Each flow pattern archetype exhibits unique scaling behavior. For most flow pattern archetypes, optimal feature size occurs at an intermediate channel dimension. Extremely small flow channels do not optimize performance despite improved mass transport. Pressure drop loss and flow travel path in the cathode compartment are major factors determining the optimal size. The scaling phenomena are explained in conjunction with the details of oxygen distribution in the cathode flow channels and gas diffusion layer. (C) 2004 Elsevier B.V. All rights reserved.