This study focuses on a determination of the cell voltage losses observed for Pt and PtRu loading reductions in H-2/air and reformate/air polymer/electrolyte-membrane fuel cells (PEMFC). Experiments with catalyst-coated membranes (CCM) of varying anode and cathode catalyst loadings with H-2/O-2, and H-2/air demonstrate that the anode catalyst loading in state-of-the-art membrane electrode assemblies (MEAs) operating on pure H-2 can be reduced to 0.05 mg(Pt)/cm(2) without significant voltage losses, while the cell voltage losses upon a reduction of the cathode catalyst loading from 0.40 to 0.20 mg(Pt)/cm(2) for optimized MEAs amounts to 10-20 mV, consistent with purely kinetic losses due to the oxygen reduction reaction. It is shown that H-2/air operation with state-of-the-art MEAs very closely approaches the Pt-specific power density (in units of g(Pt)/kW) for large-scale automotive fuel cell applications with pure H-2 feed.For reformate/air operation, PtRu anode loadings can be reduced to 0.20 mg(PtRu)/cm(2) for reformate containing 100ppm CO with a 2% air-bleed. Any further reduction will, however, require either a change in operating conditions (i.e. lower CO concentration or cell temperature much greater than 80 degreesC) or novel, more CO-tolerant anode catalysts. (C) 2004 Elsevier B.V. All rights reserved.