The kinetics of CO oxidation over an alumina supported Cu catalyst are examined using successive oxidation and reduction cycles. Experiments were done at a temperature of 493 K with isotopically labelled gases in a tubular reactor. Surface species were monitored during transients in an FTIR flow cell. For the reoxidation of the catalyst a three-step mechanistic model is proposed. The kinetic constants are determined by mathematical modelling. The role of carbonates is found to be minor in the production of CO2 in contrast to carbonyls which are shown to be the intermediates. A net dissociation of the CO bond was observed during reduction caused by adsorption of CO2 on a partly reduced catalyst under formation of carboxylates and its subsequent decomposition to CO,2 thereby leaving oxygen on the catalyst. A complete mechanistic scheme is presented which allows us to describe qualitatively and in part quantitatively the experimental results. This study shows that the use of forced oscillations is a powerful tool with strong elucidating abilities in mechanistic investigations in heterogeneous catalysis.