The restricted umbrella sampling method proposed by Shing and Gubbins was applied to calculate the solubilities of hexamethylbenzene and those of phenanthrene in supercritical carbon dioxide. It was also used to calculate solubility enhancements of phenanthrene by the addition of octane in supercritical carbon dioxide. The Lennard-Jones (12-6) potential was used as the intermolecular potential and the Lorentz-Berthelot mixing rule was adopted for unlike molecular pairs. The solubilities of phenanthrene and those of hexamethylbenzene in supercritical carbon dioxide were calculated quantitatively by introducing only a binary interaction parameter between unlike molecules. Furthermore, the entrainer effects calculated by the Monte Carlo simulation show good agreement with the experimental data.