Acetoxyldation processes are a special type of oxidation process in which the oxygen participates indirectly in the coupling of olefins and carboxylic acids. For example, propylene, acetic acid, and oxygen were catalyzed by Pd catalyst at 433.15 K, 0.5-0.6 MPa to form allyl acetate. As a part of developing safe propylene acetoxylation processes, the effects of excess oxygen are studied directly in the presence of a catalyst or an ignition source. Oxidation and combustion arefiound to dominate the catalytic reaction when the oxygen feed concentration exceeds the normal level of 6.4%. Temperature runaway is found to occur at feed oxygen concentrations > 14%. Without the presence of catalysts. The ignition and deflagration are possible only when the feed oxygen concentration is > 18.6%. The possible mechanism of the catalytic combustion is discussed. The results suggest that using homogeneous flammability limits as the safe operating boundary for catalytic gas-phase acetoxylation processes is unsafe and proper precautions must be taken fior potential catalytic oxidation. (c) 2005 American Institute of Chemical Engineers Process.