We investigated electrochemical behavior of surface oxides of platinum formed by annealing in air. We studied the catalytic activity for CO electrooxidation using electrochemical, X-ray, and DFT methods. We find that all oxidized platinum surfaces are highly active initially for CO electrooxidation reaction in so-called preignition region. While the high activity of the monolayer oxide formed on extended Pt surfaces decreases after the initial CO-oxidation cycle, bilayer oxide formed on nanoscaled facets sustain the high CO electrooxidation activity. DFT calculations show that OH binds, as strongly to bilayer surface oxides as to metallic surface while CO does not, suggesting the bifunctional property of the bilayer oxide surface. Published by Elsevier Ltd.