Oxidative dehydrogenation, ODH of propane and ethane was studied on VOx/SiO2 (VSi) and VOx/MgO (VMg) catalysts of the same vanadium loading (1.5 theoretical monolayer of vanadia) and doped with additives of main group elements (K and P) and of transition metal ions (Ni, Cr, Nb, and Mo). The additives modify both the specific activity and selectivity to olefins, the modifying effect (its sign and extent) depending on the type of the catalyst and on the alkane nature. The main difference between the two series of the catalysts consist in: (a) increase in the specific activity in the ODH reactions on introduction of the additives (except K) for VSi and decrease for VMg catalysts, (b) considerable increase in the selectivity to propene in ODH of propane for K-doped VSi catalyst and decrease for K-doped VMg catalyst (Ni, Cr, and Mo increasing and P decreasing the selectivity for the both series), and (c) higher selectivities to ethene as compared with those to propene for VSi and lower to ethene than to propene for VMg catalysts. In contrast to the propane ODH the additives exert only very small effect on the selectivities to ethene in the ODH of ethane. (c) 2006 Elsevier B.V. All rights reserved.