In this study, DPTG (Dashtizadch-Pazuki-Taghikhani-Ghotbi) equation of state has been modified for calculation of phase behavior of fluids and solubility parameter. The accuracy of the modified EOS has been proved by estimation of the properties of some hydrocarbons such as densities of methane and condensate gases, vaporization enthalpy, sublimation pressure, compressibility factor and comparison of the obtained results with the results of the present equations of state such as NJ (Nasrifar-Jalali), ZMJL (Zhi-Meiren-Jun-Lee) and PR (Peng-Robinson). Then, the Flory-Huggins model has been modified and asphaltene precipitation phase behavior at different ratios of solvents in the crude oil has been predicted by the modified EOS and the developed Flory-Huggins model. Comparison of the obtained results with the experimental data of asphaltene precipitation and the calculated ones by the main Flory-Huggins model shows the accuracy of the developed model. (c) 2007 Elsevier Ltd. All rights reserved.