Oxidative dehydrogenation (ODH) of propane with lattice oxygen of alpha-, alpha'- and beta-NiMoO4 phases has been studied. Reduction tests of the different phases were performed by TG analysis under hydrogen at different temperatures. Under isothermal conditions lattice-oxygen-consumption rate was found to be higher on the beta-phase with respect to the alpha- and alpha'-phases. TG analyses showed the existence of different sources of lattice oxygen in the catalyst, depending on the NiMoO4 phase. Catalytic activity was measured under steady state conditions, using a periodic flow reactor and it was then correlated to the reduction curve. It was found that the activation energy for ODH reaction over NiMoO4 of 54.3-62.7 kJ/mol is nearly identical to that obtained for the catalyst reduction under hydrogen (46-50.2 kJ/mol). The correlation between the activation energy of the reaction in a periodic operating system (POS) and that of solid reduction under hydrogen suggests that the reaction obeys a red-ox mechanism.