The gas phase oxidative cracking (GOC) and non-oxidative pyrolysis of heavy hydrocarbons were investigated, with decalin (decahydronaphthalene) and tetralin (tetrahydronaphthalene) as the model compounds for naphthenic hydrocarbon and aromatic hydrocarbon, respectively. Unlike pyrolysis, the ring rupture of decalin or tetralin molecule and the decoking ability of system were significantly enhanced due to the introduction of O-2 in GOC. For GOC of decalin, both the lower alkenes and the light fuels were obtained. At lower temperatures the light fuels mainly contained alkyl benzene, alkyl cyclohexane and isoparaffins, while it was rich in BTX (benzene, toluene and xylenes) at higher temperatures. A 38.9% yield of lower alkenes and 48.0% yield of light fuels (BTX mass content: 59.9%) at 100% decalin conversion were obtained under the conditions of 800 degrees C and decalin/O-2=0.5. For GOC of tetralin, both the dehydrogenation and the cracking reactions dominated the reaction routes, resulting in a high mass content of alkyl naphthalene and alkyl benzene in the light fuels. The estimation of O-2 distribution in the products demonstrated that O-2 participated primarily in the oxydehydrogenation reactions at low temperatures, while mainly in the partial oxidation reactions at high temperatures to produce COx (x=1, 2). (C) 2006 Elsevier B.V. All rights reserved.