Quantitative measurements of CO chemisorption in the range 140–180 K, supported by FTIR data on adsorbed CO, were performed on Au/TiO₂, Au/Fe₂O₃, and Au/CeO₂ catalysts. On the first two samples, which had similar particle size distributions, an average Au/CO chemisorption stoichiometry of about 3, referred to step-edge Au atoms, was found. On Au/CeO₂, where very small clusters and quite large particles are present, the CO-chemisorbed volume was much higher than expected, due to the prevailing contribution of very small Au clusters. On the same sample, a change in the IR absorption coefficient was observed and was reasonably explained.