The serpentine flow field is the leading type of flow field used today in proton exchange membrane (PEM) fuel cells and for this reason optimization of serpentine flow field design is extremely important In this study, a unique technique developed in house is utilized to separately measure current density under the land and channel on a variety of serpentine flow field geometries Each flow field is tested under a wide variety of operating conditions thereby providing guidance for the optimum design geometry Experimental results show that generally flow fields with both thinner lands and thinner channels provide better overall performance However, the optimal flow field designs are highly dependent on fuel cell operating parameters. (C) 2009 Professor T Nejat Veziroglu Published by Elsevier Ltd. All rights reserved