The recently developed heteronuclear group contribution SAFT-VR equation (GC-SAFT-VR) [Peng et al. Fluid Phase Equilib. 2009, 227 (2), 131-144] enables the predictive study of the thermodynamic properties of fluids and their mixtures by Using a molecular-based model in which the molecules are described by heterosegmented chains in which each type of segment represents a functional group present in the molecule. Given the Success of the GC-SAFT-VR approach in predicting, the fluid phase equilibria Of mixtures without fitting to any mixture data, and the known difficulties in determining equation-of-state parameters for polymers because of the lack of coexistance data, ill this work, we extend the GC-SAFT-VR equation to Study the phase equilibria or small molecules in polymer systems. The results demonstrate the ability of the GC-SAFT-VR equation of I state to predict the vapor-liquid and liquid-liquid equilibria of polymer Solutions and accurately capture the effects of polymer molecular weight and molecular topology oil phase behavior.