Au/TiO2 catalysts are active for CO oxidation at room temperature and lower. To probe the surfaces of these catalysts, CO and O-2 adsorption and coadsorption on model Au-TiO2 systems were examined under UHV conditions using TPD, ASE and XPS. No chemisorption of molecular O-2 was detected, as previously reported for clean Au single-crystal surfaces. A low concentration of CO adsorption sites associated with Au was observed; however, no unique interfacial sites could be unambiguously identified on these surfaces.