The experimental results for the CO2-ODA system are modeled using Ping-Robinson equation of state with temperature-independent parameters. The experimental data was compared with the calculated data by Peng-Robinson equation of state for the CO2-ODA system. Phase behavior data for ternary poly(octadecyl acrylate) [PODA]-CO2-octadecyl acrylate[ODA] are measured in the temperature range of 36 to 194 ℃, to pressure as high as 2,000 bar, and with cosolvent concentrations of 11.9, 25.9. 28.0, 35.0 and 40.0 wt%. This system changes the pressure-temperature slope of the phase behavior curves from negative to positive as the cosolvent concentration increases. The addition of 45.0 wt% ODA to PODA-CO2 shows the change of LLV phase behavior. Pressure-composition isotherms are also shown for the CO2-ODA at 45, 80 and 120 ℃ and in pressure from 28 to 306 bar.