The critical points, bubble points, and dew points of ethylbenzene + CO 2 , styrene + CO 2 , and ethylbezene + styrene + CO 2 mixtures were measured in CO 2 -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 CO 2 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 CO 2 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.