The modification of graphite and titanium carbide surfaces exposed to oxygen under simultaneous 4 keV Ar + ion bombardment at room temperature was studied by means of Auger electron spectroscopy. It was found that in graphite the incorporation of oxygen is extremely small, whereas in titanium carbide it is greatly promoted by simultaneous particle impact during the exposure. For the latter case the amount of incorporated oxygen increases with increasing concurrent ion dose, showing a square root of dose dependence up to 1 × 10 16 Ar + ions/cm 2, and the oxygen incorporation extends over the whole depth of the collision cascade. Furthermore the maximum equilibrium concentration of oxygen at the top surface is limited by the highest-valence oxide, i.e. TiO 2 formed on the surface.