The effects of 3 vol.% of CO2 added in the gas feed are investigated in the oxidative dehydrogenation of propane (ODP) to propene on NiMoO4 catalysts. In spite of the low reaction temperature range (400-480degreesC), it turns out that CO2 is not inert during the reaction. CO2 behaves as a strong oxidant with respect to the catalyst. CO2 helps to maintain the catalytic surface in a high oxidation state under conditions for which NiMoO4 undergoes a reduction. CO2 clearly promotes the non-selectivity of the catalyst and can inhibit deactivation. Under particular conditions it can improve propene formation. CO2 is able to oxidize propane to propene. We suggest that CO2 dissociates during the reaction to CO and an active oxygen species, which is responsible for the oxidizing effect of carbon dioxide. This work opens promising perspectives in using CO2 to tune dynamically the oxidation state of "working" oxide surfaces in their most active and selective configurations for oxidation processes.