As for catalytic pyrolysis of Daqing atmospheric residue over catalysts LCM-5 and CEP-1, this paper investigated the effect of catalyst to oil weight ratio on gaseous product distribution in a confined fluidized bed reactor. Cracked gas was determined by gas chromatograph. The results show that the effect of catalyst to oil weight ratio on yields of gaseous products depends on the catalyst used. For LCM-5, at a reaction temperature of 973 K, steam to oil weight ratio 0.63 and residence time 1.8 s, the total yield of light olefins exceeds 50 wt.% and increases linearly with catalyst to oil weight ratio. For CEP-1, at a reaction temperature 923 K, steam to oil weight ratio of 0.75 and residence time 1.7 s, the total yield of light olefins pass through a maximum of 44 wt.% with the increase of catalyst to oil weight ratio. Experimental data are analyzed by least square method to produce experimental formulae for yields of ethylene, propylene, butylene and total olefins as a function of catalyst to oil weight ratio. Catalyst type is the key element in the pyrolysis reaction, affecting both the yields of products and the reaction mechanisms. (C) 2003 Elsevier B.V. All rights reserved.