This study has an important impact on gasoline engine-pollution control working under lean conditions. While NOx trap systems can remove NOx under an oxidative atmosphere, they are poisoned by SOx present in the exhaust gases. In order to protect NOx traps, an upstream SOx trap has to be used. SO2 adsorption was studied in the presence of water and oxygen. Model and commercial catalysts were tested between 300 and 700degreesC. In order to assign the TPD peaks, the decomposition of commercial sulphates was studied versus the temperature. Adsorption capacity is not sensitive to oxygen and SO2 concentrations but is strongly related to barium content. Cerium content is not a key parameter for SO2 adsorption capacity in the presence of oxygen. XPS analysis allowed us to differentiate between all the species formed during the adsorption process. When the catalysts are aged, specific surface area decreases as well as adsorption capacity.