In this work, a simplified thermodynamic modeling procedure for determination of the amount of asphaltene precipitation is presented. The onset of asphaltene precipitation in the presence of different solvents is predicted by applying the molecular solubility model. Since asphaltene molecular weight varies in different solvents, the molecular weight of asphaltene has been tuned by experimental data. The tuned molecular weight is used to predict the amount of precipitated asphaltene. The Flory-Huggins statistical thermodynamics theory is applied to derive the Gibbs free energy relationship. A necessary and sufficient condition is defined to minimize the Gibbs free energy relation. By solving the set of equations derived from the minimization, the weight percent of precipitated asphaltene has been determined. The advantage of this model is that one does not need to perform expensive and time consuming experiment in order to obtain molecular weight data. The other improvement of this model compared to the other models is the requirement of a minimum amount of experimental data to find the unknown parameters. It also has the advantage of obtaining solubility parameters through thermodynamics relationships rather than using the relation for regular solution when the asphaltene solution is a non-regular solution. The results of this model are in good agreement with the experimental data. (c) 2006 Published by Elsevier Ltd.