In this study we examine photostimulated reactions taking place on the surface of wide band-gap metal oxides such as ZrO ₂ and TiO ₂. In particular, we explore the photostimulated adsorption (PhA) of oxygen on ZrO ₂ upon illumination with UV light (λ < 260 nm) and its postphotostimulated photoadsorption (PPSPhA) on irradiation with visible light (λ > 400 nm). The emphasis is on an examination of the decay channels of PhA-active surface centers to rationalize the interdependencies of the rate r(p,p) on pressure and light intensity The distinguishing feature of O ₂ PhA kinetics, dp/dt ∝ p ^mp ⁿ, resides in the dependence of the order of the reaction on the order m with respect to photon flow (p ^m) and on the order with respect to pressure (p ⁿ). In other words, m → 1 if → 0 whereas n →1 if m →0. The reaction orders m and n are interdependent in the case of PhA of O ₂ on ZrO ₂. A general mechanism is described for the several stages implicated in both PhA and PPSPhA surface processes. A preliminary consideration is also given to expand the PhA pathway for O ₂ on ZrO ₂ to processes that take place in the photocatalyzed oxidation of phenol in irradiated TiO ₂ aqueous dispersions and the interdependence of the rate of the photoreaction on the concentration of phenol and on the incident light intensity.