The selective oxidation of CO on Au/Al2O3 and Au/Mo-x/Al2O3 OM = Mg, Mn) in the presence of H-2 was studied. The addition of MgO and MnOx improves the CO oxidation activity and selectivity towards CO2. The beneficial effect of MgO can be ascribed to stabilization of small Au particles, which are intrinsically more active in CO and H-2 oxidation. MnOx is thought to be able to supply the active O needed for CO oxidation. Au catalysts containing both MgO and MnOx are extremely active in CO oxidation. In the presence of H-2 selectivity towards CO2 higher than 0.90 was observed for Au/MgO/Al2O3 and Au/MnOx/MgO/Al2O3 at 100 degreesC and below The H-2 oxidation at low temperature was affected by adsorbed CO. At temperatures above 50 degreesC the thermal desorption rate of CO was large enough for H-2 oxidation to commence, implying a decrease in selectivity. Besides H-2, water was also found to have a pronounced effect on the CO oxidation rate even at room temperature. The effect of water is ascribed to a beneficial role of surface OH groups in CO oxidation.