This study presents a new method to quantitatively determine the electrocatalytic activity of Vulcan carbon and Vulcan-supported Au nanoparticles, dispersed as catalyst thin films on glass carbon, for oxygen reduction in an aprotic electrolyte using rotating disk electrode measurements. The ORR activity of Vulcan carbon can be described by a Tafel slope of 120 mV/ dec and Levich-Koutecky analysis of Vulcan carbon suggests that solvated LiO2 is the initially formed O-2 reduction product. Discharge voltages extrapolated from this thin-film method are in excellent agreements with those of Li-oxygen batteries demonstrating its validity to serve as an effective technique for catalyst screening. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3555071] All rights reserved.