Current density and potential distribution measurements were conducted using a segmented current collector and flow field setup on membrane electrode assemblies prepared with segmented and unsegmented electrodes made from two different types of commercially available gas diffusion layers. Both galvanostatic and potentiostatic discharge modes were employed. Irrespective of the type of gas diffusion layer, when a common electrode was employed, significant performance variations were encountered between current collector segments in the constant voltage mode, while the segment to segment variations were minimal in the constant current mode. Both types of discharge modes showed negligible variations between segments in the case of segmented electrode. A simple mathematical model was developed to assist in the interpretation of the experimental results. The differences in contact resistances between the current collectors and the gas diffusion layer, especially on the cathode side have been identified as the primary reason for the experimentally observed behavior. Based on the results presented here, segmenting the electrode along with the current collector is recommended for current distribution studies. When using a common electrode, only the galvanostatic mode is preferred to minimize contact artifacts. (C) 2004 Elsevier B.V. All rights reserved.