The thermodynamics of oxygen desorption from TiO2 crystals under steady light excitation is investigated. The non-equilibrium photo-induced processes are explicitly accounted for by considering the rate of entropy production. The adsorption/desorption properties of oxygen on anatase nanocrystals are investigated as a function of the pressure of the experimental room and a generalized Langmuir–Fowler equation is obtained for the case of photo-assisted surface processes. The kinetic scheme used for this study involves color centers and surface centers on the Ti3C sites. In particular, oxygen depletion is forced by recombinations of electrons trapped in bonding sites and holes trapped in color centers (FC centers).