Gas oil cracking experiments in the presence of steam were performed in a loboratory-scale tubular quartz or Inconel reactor. The effects of temperature, inlet steam to gas oil ratio, and residence time on the major effluent products were investigated. The temperature, steam to gas oil weight ratio, and residence time were varied in the ranges 628-800 {degrees}C, 1-2 kg/kg, and 0.4-1.0's, respectively. The best yield of ethylene, 27% by weight, was obtained in the quartz reactor at 770 {degrees}C, residence time of 0.6 s, and mass ratio of steam to gas oil equal to 1. Experiments combined with a simulation model allows the authors to predict the effluent products distribution as a function of temperature and residence time. Several kinetic models were attempted. The best one was a mechanistic radical and molecular model. Gas oil feedstock composition was simplified, taking into account radical and molecular model. Gas oil feedstock composition was simplified, taking into account one compound as representative of the principle hydrocarbon families. For this study, the model proposed consisted of 138 reactions, 18 species, and 24 radicals.