The enhancing effect of sulphate ions added to titania supports for the oxidation of carbon monoxide, catalyzed by gold, supported on the titania has been shown to be generally applicable to more than one type of titania. It seems from examining the characterization and catalytic data that the sulphate promotional effect is mainly due to a direct chemical effect on catalytically active sites. (C) 2008 Published by Elsevier B.V.