In the absence of tetrachloromethane (TCM) carbon dioxide is the principal product formed in the oxidation of propane on ceria. The introduction of small partial pressures of TCM increases the conversion of propane with selectivities to propene up to 80%. Except under special circumstances no evidence of chlorinated species from TCM is found in the bulk structure while the surface region is shown to contain chlorine, although its form is not known. The enhancement of conversion and selectivity to propene is shown to be dependent upon the presence of chlorine, in whatever form, in the surface region of the catalyst. (C) 2000 Academic Press.