The kinetics of the oxidation of carbon monoxide by oxygen have been studied in the temperature range 0 < theta < 80 degrees C on alumina-supported Pt/SnO2 catalysts, the respective areas of the two active compounds being varied independently of each other. Rate measurements have been performed as well as titration experiments. The results indicate that the chemisorption of CO is restricted to platinum, whereas oxygen is adsorbed on both Pt and SnO2. The rate pattern may be described by a mechanism where the migration of adsorbed species is added to the classical elementary reaction sequence of CO oxidation on platinum. Monte Carlo simulations show that the proposed mechanism can explain the experimental results. Under conditions where the rate is zero order with respect to both CO and O-2. Simulation indicates that the migration rate of oxygen could be the determining step. Oxygen spillover from SnO2 to Pt cannot be excluded but is not necessary to describe the experimental results.