Vanadium-molybdenum oxides supported on alumina were prepared by successive wet-impregnation, in order to evaluate their activity in oxidative desulfurization (ODS) of sulfur compounds prevailing in diesel fuel. The oxidation states and reducibility of the catalysts were studied by means of reduction-oxidation cycles of temperature programmed, and chemical-quantitative analyses by permanganometric and ferrometric titrations, for fresh as well as used catalysts. Redox cycles were performed, involving TPR analyses separated by an oxidation treatment (TPO), which were carried out consecutively before or after ODS-batch cycles. ODS tests were carried out comparing oxidant performance of tertbutyl hydroperoxide and H(2)O(2). TPR of the catalysts makes possible to have vanadium-oxides with different degree of reduction, which were correlated with ODS activity. According to these results vanadium-oxide species with 12.9% of reduction showed higher ODS performance. (C) 2009 Elsevier B.V. All rights reserved.