The critical points, bubble points, and dew points of ethylbenzene + CO2, styrene + CO2, and ethylbezene + styrene + CO2 mixtures were measured in CO2-rich region, and the density of the mixtures were also determined. For all the mixtures, the critical temperatures and critical pressures increase with the decrease Of CO2 concentration in the concentration range studied. The phase separation pressures of the mixtures increased with increasing temperature at a fixed composition, but at constant temperature the phase separation pressures decreased as the CO2 mole fraction in the mixtures was reduced. The Peng-Robinson equations of state was used to calculate the critical points, bubble points, and dew points parameters. The results agreed reasonably with the experimental data. The isothermal compressibility (K-T) of the mixtures was also investigated. It is demonstrated that the trend of K-T to pressure varies slowly as the pressure is far from the phase separation points. However, K-T is sensitive to pressure and reaches the maximum as the pressure approaches to the phase separation points. At the critical temperatures, K-T varies more significantly with pressure than that at bubble points and dew points.