Heavy oil upgrading and ultra-clean fuel production are critical matters for petroleum industry. Processes must be engineered both to increase refinery efficiency and to protect the environment. Kinetic models of FCC were generated and examined. Software for the computer generation of kinetic models was exploited to generate an optimum set of elementary steps corresponding to a mechanistic kinetic model for the catalytic cracking of vacuum gas oils. The kinetics model building program uses graph theoretic concepts to represent the molecules as atomic connectivity matrices and the reactions as matrix operations. The rate constants for each reaction family were constrained to follow the Evans-Polyani relationship, which, for each reaction family, relates the rate constant to the enthalpy of reaction. This helped to reduce both the complexity of the reaction network and the number of rate parameters to be optimized. The comparison of model outputs and experimental measurements is favorable. This is an abstract of a paper presented at the AIChE Annual Meeting and Fall Showcase (Cincinnati, OH 10/30/2005-11/4/2005).