The role of water vapor was explored for the partial oxidation of propene over antimony-tin-vanadium oxide (SB/Sn/V oxide) catalyst at 1 atm pressure and 340 degrees C using a microcatalytic packed bed reactor, Steady-state, transient kinetics, TPD, and isotopic transient experiments were performed, Water suppresses the formation of CO2 by blocking the most active sites which are responsible for CO2 formation but water also enhances the rate of the catalytic oxidation by keeping the catalyst surface at a high oxidation state and preventing the formation of strongly bonded oxygenates, Isotopic transient experiments with labeled O-2 in the presence of water indicate a strong interaction between water and the catalyst surface, Water exchanges oxygen slowly with the surface of the catalyst.