Mutual solubilities of a mixture containing 80.52% ethanol and 19.48% octane were measured in a carbon dioxide solvent using a high-pressure type phase equilibrium apparatus at pressures up to 100 bar and at a temperature of 75°C. Experimental results showed that a considerable separation was not achieved in the ethanol-octane ratio investigated in this work. The experimental data were then compared with the theoretical data which were obtained from the regular solution equations. Regular solution theory was employed for each phase by applying activity coefficient expressions. The regular solution theory approach has been found to be encouraging for the prediction of solubility data (vapor phase data) and also showed that the interaction parameters were dependent on pressure.