Using density-functional theory combined with surface thermochemistry, the effects of sulfo-reductive conditions (PH2O, PH2S, PH2, and T), including those prevailing in the industrial process of hydrodesulfurization (HDS), are investigated for two catalytic supports: anatase-TiO2 and gamma-Al2O3. It is found that under the usual HDS conditions, H2S may partially sulfide the (001) surface of anatase-TiO2, leading to the formation of mu(2)-S species together with two hydroxyl groups. The (110) surface of gamma-Al2O3 is sulfided only if the water pressure is very low, leading to the formation of sulfhydryls and hydroxyls. The effect of H-2 pressure is also addressed. A comparison with published experimental data (such as TPR, IR, XPS) is supplied. (C) 2004 Elsevier Inc. All rights reserved.