Temporal Analysis of Products (TAP) reactor system was used to investigate CO oxidation behavior on Au/SiO2 catalysts prepared via the physical vapor deposition method of magnetron sputtering. Au/SiO2 catalysts are a valuable model system for studying the reactivity of Au nanoparticles, as the SiO2 support plays little role in the reaction. The adsorption of CO on the catalyst was studied at different temperatures under TAP vacuum conditions. The heat of CO adsorption estimated from TAP results by moment analysis is -24.39 +/- 3.70 kJ/mol. Multipulse TAP experiments showed the important dependency between the oxygen pretreatment pressure (UHV to 33.66 psia) and catalytic activity for CO oxidation. The observed kinetic behavior indicates that oxygen consumed by CO can be replenished by oxygen stored in a reservoir, which is filled during pretreatment. The oxygen pretreatment pressure determines the amount of oxygen stored in the reservoir. The kinetic behavior indicates that oxygen is stored in the gold subsurface or at the Au/SiO2 interface, and that the active oxygen species is atomically adsorbed oxygen.