An approach combining the Peng-Robinson equation of state and novel solvation free energy calculation is developed here to describe the liquid-liquid equilibria for highly nonideal mixtures. This method has been previously shown to provide reliable vapor-liquid equilibria of pure and mixture fluids. The hydrogen-bonding interaction in this model is refined in order to properly describe the variation in the strength of hydrogen bond between different types of species. This method contains only 15 global parameters and 3 element-specific parameters (one atomic radius and two for the dispersion energy), and can be used to predict the miscibility gap of liquid mixtures and its temperature variations without sacrificing its capability in predicting vapor-liquid equilibria. The overall root-mean-square error in the mutual solubility of 68 binary mixtures predicted from PR+COSMOSAC is 0.0689, compared to those from the Modified UNIFAC 0.0822 and UNIFAC-LLE 0.0697, respectively.