Pressure-composition isotherms are obtained for carbon dioxide (CO2)-hexyl acrylate and CO2-hexyl methacrylate systems at 40, 60, 80, 100, and 120 degreesC and pressure up to 189 bar. The CO2-hexyl acrylate and CO2-hexyl methacrylate systems exhibit type I phase behavior with a continuous mixture critical curve. Three-phase, liquid-liquid-vapor equilibrium was not observed at these conditions. The experimental results for CO2-hexyl acrylate and CO2-hexyl methacrylate mixtures are modeled using the Peng-Robinson equation of state. A good fit of the data is obtained with the Peng-Robinson equation of state using two adjustable parameters for CO2-hexyl acrylate and CO2-hexyl methacrylate systems. Experimental cloud-point data to 200 degreesC and 2200 bar are measured for binary and ternary mixtures of poly(hexyl acrylate)CO2-hexyl acrylate and poly(hexyl methacrylate)-CO2-hexyl methacrylate systems. Also, the cloud-point curves show the binary mixtures for poly(hexyl acrylate) in supercritical ethylene, propane, propylene, butane, 1-butene, chlorodifluoromethane, and dimethyl ether. The phase behavior for the system poly(hexyl methacrylate)-CO2-hexyl methacrylate is measured in changes of the pressure-temperature slope and with cosolvent concentrations of 0, 9.2, 14.4, and 32.4 wt %. With 43.8 wt % hexyl methacrylate to the poly(hexyl methacrylate)-CO2 solution significantly changed, the phase behavior curve takes on the appearance of a typical lower critical solution temperature (LCST) boundary. The cloud-point curves for the poly(hexyl acrylate)CO2-0, 5.0, 12.8, and 20.7 wt % hexyl acrylate system change the P-T curve from the upper critical solution temperature region to the LCST region as the hexyl acrylate concentration increases. Adding 33.9 wt % hexyl acrylate to the poly(hexyl acrylate)-CO2 solution significantly changes the phase behavior. The cloud-point curve takes on the appearance of a typical LCST region.