The production of biofuels from cottonseed oil by fixed-fluidized bed catalytic cracking at ambient pressure was studied. The effect of reaction temperature (400-500 degrees C), catalyst-to-oil ratio (6-10)and residence time (50-90 s) were Studied over the yields of bio-gasoline and light fuel oil (<= 360 degrees C). Design of experiments was used to study the effect of operating conditions over yield of hydrocarbon fuel. The response Surface methodology was used to determine the optimum values of the operating variables for maximum yield of biofuels in the liquid product obtained. (C) 2008 Elsevier Ltd. All rights reserved