The interaction between CO and Pt/ceria catalysts was investigated by oxygen storage capacity measurements, CO and CO2 isotope exchange and FT-IR measurements. A Pt/alumina sample was also investigated for comparison. The capacity to store and release oxygen as a function of ceria surface-area and Pt-ceria contact was estimated. The presence of chlorine from the Pt pre-cursor was found not to decrease the oxygen storage capacity. However, FT-IR measurements showed that chlorine hindered the carbonate formation during CO exposure, which was found to be the main form of carbon storage on the pre-oxidized sample. On a strongly reduced sample, CO disproportionation was found to occur to an increasing extent with increasing degree of reduction. CO and CO2 isotope exchange showed that these molecules exchange their oxygen with Pt/ceria and ceria quite easily at 400 degrees C. CO chemisorption at -78 degrees C as a method to determine the metal dispersion was also investigated. At this temperature, the CO uptake on ceria was strongly suppressed, especially on the Cl-free sample, but not completely hindered.