Abstract: The role of lattice oxygen in the catalytic dehydrogenation of ethylbenzene over industrial iron-oxide-based catalysts has been investigated mainly by means of isotopic exchanges attending the dehydrogenation reaction.The results indicated that although the exchange of lattice oxygen with steam oxygen appeared to take place to an appreciable extent, the direct catalytic dehydrogenation of ethylbenzene appeared to be the major reaction pathway, with catalytic dehydrogenation by oxygen-transfer reaction pathway playing only a minor role, as revealed different extents of hydrogeh-deute-rium isotopic exchange between ethylbenzene and steam D₂Q at low and very high space velocities.The mechanisms of these two reaction pathways are discussed.For the oxygen-transfer dehydrogenation mechanism, electron transport between neighboring Active-sites operating cooperatively in opposite phases of their redox cycles may be a requisite factor.