The precipitation of waxy constituents in petroleum mixtures subjected to a cold environment gives rise to a variety of problems well-known in the petroleum industry. A revised multi-solid phase thermodynamic model for predicting wax precipitation in petroleum mixtures is presented in this article. The Peng-Robinson equation of state is used to evaluate the phase behavior of both liquid and vapor phases. The results predicted by this model agree with the experimental data of wax precipitating for several synthetic oils and crudes.