The interaction of CO and O-2 with Au/TiO2 and Au/Al2O3 catalysts is studied with EPR spectroscopy. Adsorption of CO and O-2 can produce at room temperature in both fresh catalysts O-2(-) radicals stabilized on support cations (suggesting a spillover process exists at least in Au/Al2O3); thus, O-2(-) generation does not require a reducible support. These O-2(-) species react upon CO addition giving diamagnetic species. CO adsorption at room temperature on freshly activated Au/TiO2 abstracts oxygen ions from the support surface producing Ti3+ anion vacancy centers, but after the specimen has interacted with both O-2 and CO a new CO adsorption gives (reversibly, suggesting easy Au-titania electronic interaction) only fully coordinated Ti3+ unable to stabilize O-2(-); this indicates coverage of Ti active centers by reaction products (e.g., carbonate or peroxide species) which are not eliminated by CO or O-2. The results indicate that steady state catalytic CO oxidation on Au/TiO2 may proceed without involving Ti-stabilized O-2(-).