An Fe-oxide promoted Pt/gamma-alumina catalyst, highly active and selective for the oxidation of CO in H-2, has been studied by a combination of electron microscopic and spectroscopic techniques. The goal of the study is to understand the role of Fe in promoting the activity of the catalyst for this reaction important for purifying the H-2 for solid polymer electrolyte fuel cell applications. The results show that the promoter Fe oxide must be in intimate contact with the Pt to enhance high CO activity. The Fe oxide partially covers the Pt metal surface, interacts with the Pt particles and changes the electronic properties of the Pt metal particles. The Fe oxide provides oxygen to the CO adsorbed on the Pt thereby creating a dual site non-competitive mechanism for CO oxidation. The uniqueness of this arrangement enhances the catalytic activity for selective CO oxidation relative to Pt only catalysts in hydrogen streams.