Pressure-composition isotherms were measured for the CO2/octadecyl acrylate system at 45.0, 80.0, and 100.0degreesC and at pressures up to 307 bar. This system exhibited type I phase behavior with a continuous mixture-critical curve. The solubility of octadecyl acrylate for the CO2/octadecyl acrylate system increased as the temperature increased at a constant pressure. The experimental results for the CO2/octadecyl acrylate system were modeled with the Peng-Robinson equation of state. A good fit of the data was obtained with the Peng-Robinson equation of state with one adjustable parameter for the CO2/octadecyl acrylate system. Experimental cloud-point data for the poly(octadecyl acrylate)/CO2/octadecyl acrylate system were measured from 36 to 193degreesC and at pressures up to 2100 bar, and the added octadecyl acrylate concentrations were 11.9, 25.9, 28.0, 35.0, and 40.0 wt %. Poly(octadecyl acrylate) dissolved in pure CO2 up to 250degreesC and 2100 bar. Also, adding 45.0 wt % octadecyl acrylate to the poly(octadecyl acrylate)/CO2 solution significantly changed the phase behavior. This system changed the pressure-temperature slope of the phase-behavior curves from an upper critical solution temperature (UCST) region to a lower critical solution temperature region as the octadecyl acrylate concentration increased. Cloud-point data to 150degreesC and 750 bar were examined for poly(octadecyl acrylate)/C2H4/octadecyl acrylate mixtures at octadecyl acrylate concentrations of 0.0, 15.0, and 45.0 wt %. The cloud-point curve of the poly(octadecyl acrylate)/C2H4 system was relatively flat at 730 bar between 41 and 150degreesC. The cloud-point curves of 15.0 and 45.0 wt % octadecyl acrylate exhibited positive slopes extending to 35degreesC and approximately 180 bar.