The interchange between the Pt-Ni-Pt and Ni-Pt-Pt bimetallic configurations in O-2 and H-2 is confirmed experimentally at atmospheric pressure using in situ X-rayabsorption spectroscopy (XAS). The subsurface Pt-3d-Pt structure, a desirable configuration as cathode electrocatalysts for PEM fuel cells, is found to be preferred in the reducing environment of H2 Whereas the surface 3d-Pt-Pt configuration is preferred in O-2. This process has been found to be reversible, providing useful insights into the maintenance and regeneration of the desirable subsurface structure. (C) 2009 Elsevier B.V. All rights reserved.