The reactivity of lattice oxygen of vanadium oxide catalysts was studied with the oxygen isotopic exchange reaction. The reactivity of pure V2O5 is compared with the reactivity of Li0.33V2O5, V2O5/TiO2, V2O5/Al2O3, V2O5/SiO2, delta-VOPO4, and (VO)(2)P2O7. According to their behaviour in the oxygen exchange reaction, two types of vanadium oxide catalysts could be distinguished. The first type of catalysts only showed exchange activity in the R-2 exchange mechanism and the second type showed activity in both the R-1 and R-2 exchange mechanisms (mechanisms in which, respectively, one or two oxygen atoms of the gas phase molecule are exchanged with oxygen atoms of the metal oxide). The catalysts which belong to the first group are bulk V2O5 and delta-VOPO4 and the catalysts which belong to the second group are Li0.33V2O5, V2O5/TiO2, V2O5/Al2O3, V2O5/SiO2, and (VO)(2)P2O7. If only the R-2 mechanism is observed then diffusion of lattice oxygen is probably faster than when both the R-1 and R-2 mechanisms are observed. The activity of the supported vanadium oxide catalysts in the oxygen exchange reaction is dependent on the support. The reactivity order is V2O5/TiO2 > V2O5/Al2O3 similar to V2O5/SiO2.