Three Pt1-xNix catalyst compositions, with high Ni content, were sputter deposited onto 3M Company's Nano-Structured Thin Film catalyst support to determine whether the high oxygen reduction reaction (ORR) activities recently reported are a surface phenomenon or require bulk Ni dissolution. The electrodes with Pt0.27Ni0.73 throughout had the highest mass specific ORR activity of the samples tested. When some of the Pt0.27Ni0.73 was replaced with either Pt or Pt0.75Ni0.25, the mass activity dropped. These results confirmed that continuous high Ni content is required to obtain high mass activity. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3595747] All rights reserved.