VAPEX reduces the viscosity of heavy oil by injecting it with a light hydrocarbon solvent. The resulting diffusion and mass transfer are strongly dependent on the injection rate, solvent concentration, cementation factor, and other reservoir parameters. The aim of this project is to modify the relationships between these parameters using laboratory test results and actual field data in order to improve the accuracy of the predictive mathematical models, since results obtained from laboratory data deviate considerably from real field behaviour.