The existence of stable V2O5 compounds as gas-phase cluster, single crystal or as supported catalyst has motivated the present work aiming at characterizing the chemical reactivity of the different aggregated moieties. We apply the concepts of electrostatic potential and Fukui function, based on periodic calculations, to explain the different chemical reactivity found for oxygen sites in V2O5 systems. Qualitative and quantitative parameters are derived for such analysis. It is found that the so-called active site is not unique, reconciling the hypotheses proposed in the literature. Coverage and support effects strongly modify the reactive regions. (C) 2008 Elsevier B.V. All rights reserved.