In this study, we report on the structure-to-property relationship for PtSn ethanol electrooxidation catalysts in alkaline and acid environment. Relationship between surface chemistry, as determined by XPS and electrochemical performance in both acid and alkaline media, is facilitated by multivariate analysis. Upon transitioning from acidic to an alkaline environment, changes in the material structure and electrochemical reaction mechanisms are observed. Electrocatalysts containing larger particles with larger relative amounts of metallic Pt and Sn perform better in acid indicating inner-sphere electron transfer reaction on active PtSn alloy phase. PtSn electrocatalysts containing larger amounts of oxidized Pt and Sn perform better in alkaline indicating that hydroxyl species that are natively present on oxidized Pt and Sn are promoting an outer-sphere electron transfer. (C) The Author(s) 2015. Published by ECS. All rights reserved.