Temperature-programmed desorption (TPD) has been used to compare the O-2 desorption characteristics of a thin film of ceria prepared by vapor deposition on an alpha-Al2O3(0001) substrate with that of a CeO2(111) surface. On CeO2(111), there is no substantial desorption of O-2 below similar to 1300 K, while a low-temperature state, between 800 and 1250 K, was observed from the ceria film. Reexposure of the ceria film to O-2 above 600 K repopulated this desorption feature, showing that adsorption-desorption cycles did not alter the morphology of the film. By adding Rh to the ceria film and then measuring the reaction of adsorbed CO on the Rh, it was demonstrated that this low-temperature feature is responsible for the oxidation of CO during TPD. The implications of these results for understanding the oxygen storage function of ceria-supported catalysts are discussed.