The model catalysts Au/Al2O3, Au/ZrO2, and Au/TiO2 were produced by laser vaporization of a metallic gold rod followed by deposition of the formed clusters onto the support powders. This technique allows to obtain a narrow size distribution of highly dispersed gold particles on the support and, most importantly, similar sizes whatever the support. This makes it possible to accurately study of the influence of the support identity on the catalytic reaction. A detailed investigation of the preferential oxidation of CO in the presence of H2 was undertaken. Catalytic performances in the PROX reaction were compared with those in the oxidation of CO in the temperature range of 25–420 °C. A boost in the conversion of CO was observed in the presence of H2 at low temperature; the extent of this boost is dependent on the support identity. Hence the reactivity order found for CO oxidation (Au/Al2O3 ≪ Au/ZrO2 < Au/TiO2) was changed. In fact, in the presence of H2, the reaction rates for the oxidation of CO become rather similar on all three systems.