The surface properties of the V-P-O-based catalysts are discussed referring to their reactivity towards different organic substrates. Various saturated and unsaturated hydrocarbons were fed under aerobic and anaerobic conditions, and the results were discussed in terms of the main surface characteristics of the active component, the vanadyl pyrophosphate (VO)(2)P2O7. The combination of acid and oxygen-insertion properties of the vanadyl pyrophosphate makes several contemporaneous reactions possible, and the final products distribution is a function of (i) the reaction conditions, which also affect the average oxidation state of vanadium, (ii) the extent of the interaction between the hydrocarbon and the surface, and (iii) the tendency of the activated hydrocarbon to undergo acid-catalysed transformations rather than oxidative ones.