The reaction Of C2H6 with lattice oxygen, O2- (in the absence of gaseous oxygen), or "adsorbed" oxygen (in the presence of gaseous oxygen) over NiMoO4 catalysts has been performed and compared to C3H8 activation. The results obtained indicate that adsorbed oxygen exhibits a higher reactivity to C2H6, while lattice oxygen is more reactive relative to C3H8. Kinetic studies of these two reactions in presence of molecular oxygen have indeed shown that the ethane oxidative dehydrogenation (ODH) is dependent on the oxygen partial pressure, whilst on the contrary propane ODH is not. In order to confirm the presence of "adsorbed" oxygen for ethane activation, ODH tests have been performed with N2O. On increasing temperature, the O- adsorbed species enhances the mild oxidation of ethane. The activation energy of ethane consumption E-C2H6, relative to propane (E-C3H8 = 133 kJ/mol) is 145 kJ/mol. A possible mechanism is proposed for the oxidative dehydrogenation of ethane.