The activation of oxygen reduction reaction fascinates numerous scientists in the fields of heterogeneous catalysis, electrochemistry and surface science. Indeed, oxygen dissociation is considered usually as the rate determining step of several reactions on conventional platinum catalysts. From combined experimental and theoretical approaches, we demonstrate comprehensively how tailored platinum-tin alloy surfaces allow to go beyond this chemical limitation. Near-ambient pressure kinetic measurements show the outstanding capacity of the Pt3Sn(111) single-crystal surfaces for carbon monoxide oxidation. The apparent activation energy is almost twice lower on the platinum-tin surface than on pure platinum catalyst. The theoretical analysis based on density functional theory calculations supports the idea that oxygen dissociation is never the rate determining step on these alloy surfaces since the corresponding rates calculated at room temperature always outstrip those of carbon monoxide oxidation. The influence of surface tin content and oxygen coverage on the activity is addressed in details. The mediatory role of tin in the alloy is elucidated on the basis of a charge transfer analysis. (C) 2010 Elsevier Inc. All rights reserved.