The influence of sulfur dioxide on methane oxidation over ceria supported platinum catalysts under lean conditions has been studied by transient flow reactor and in situ Fourier transform infrared spectroscopy experiments. The results show that sulfur dioxide can promote the oxidation of methane, here between 300 and 450 degrees C, although, as a function of time on stream, the promoting effect diminish and instead the methane oxidation becomes inhibited. We suggest that sulfate formation on ceria creates oxygen vacancies in the ceria that govern oxygen spillover leading to a lowering of detrimental oxygen coverage of platinum and/or decomposition of platinum oxide facilitating the dissociative methane adsorption. Eventually the ceria becomes saturated with sulfates and the oxygen dynamics in the platinum-ceria system settles. As a consequence, the system regresses towards highly oxidized platinum and/or otherwise active sites on the ceria or platinum-ceria boundary become blocked, which may explain the long-term inhibiting effect by SO(2) exposure. (C) 2011 Elsevier Inc. All rights reserved.