La0.8Ba0.2Fe0.4Mn0.6O3-delta (LBFMO) perovskite oxide has been found to be an active catalyst for oxidative dehydrogenation of ethylbenzene working with a characteristic Mars-van Krevelen redox mechanism in which steam functions as an oxidant. Results of this study showed that LBFMO oxide exhibited higher activity in the presence of both steam and gaseous oxygen compared with that of steam redox system. The reaction rate of oxidative dehydrogenation of ethylbenzene was zero-th order in oxygen partial pressure and 1.3 order in the amount of the surface lattice oxygen, which demonstrates that the reaction proceeded with redox system and the activity was determined mainly by the available amount of surface lattice oxygen. Kinetics of regeneration of the lattice oxygen from both steam and gaseous oxygen were also investigated, which confirmed that steam and gaseous oxygen mutually function as the oxidant for lattice vacancy on LBFMO. Results of thermogravimetric analysis showed that the available amount of the lattice oxygen in the presence of both steam and gaseous oxygen was 115 mmol mol-cat(-1), almost twice as high as that in steam alone (63 mmol mol-cat(-1)). High activity in the presence of both steam and oxygen is attributable to the fact that these can simultaneously perform as the oxidant leading to a rich amount of the surface lattice oxygen of LBFMO oxide during the reaction. (C) 2013 Elsevier B.V. All rights reserved.