Pt/CoOx/SiO2 catalysts consisting of 5 wt% Pt and 3 wt% Co3O4 are highly active for CO oxidation below 100 degrees C, In the present study the technique of temporal analysis of products was used to obtain information on the mechanism of the high activity, The behaviour of a 3 wt% CoOx/SiO2 and a 5 wt% Pt/SiO2 catalyst was compared with that of a Pt/CoOx/SiO2 catalyst. Several models proposed to explain the high activity of the Pt/CoOx/SiO2 catalyst are discussed.