The available models used for the prediction of phase behavior of hydrocarbon mixtures containing light hydrocarbons diluted in heavy petroleum fractions show some limitations in the evaluation of binary interaction parameters needed for a correct description of phase equilibria. The combined use of an equation of state including normal boiling point reference and the application of a new method based on group contribution approach gives very good results. Prediction of recent Henry's constants data of light hydrocarbons in high molecular weight hydrocarbons was successfully suggested for the check of reliability of the model.