Experimental cloud-point curves for poly(dodecyl methacrylate) [P(DDMA)] + dodecyl methacrylate (DDMA) or dimethyl ether (DME) in supercritical CO2 are reported for the binary and ternary mixtures up to 473 K and 248.0 MPa. The location of the P(DDMA) + CO2 cloud-point curve shifts to lower temperatures and pressures when DDMA or DME is used as a cosolvent. P(DDMA) does not dissolve in pure CO2 to the temperature of 493 K and the pressure of 260.0 MPa. High-pressure phase behavior data ire presented for the CO2 + DDMA system at 313.2-393.2 K and up to ca. 25.2 MPa. The system exhibits type-1 phase behavior with a continuous mixture-critical curve, and the system is adequately modeled with the Peng-Robinson equation of state. High-pressure phase behavior data are reported for P(DDMA) in supercritical propane, propylene, butane, and 1-butene. Cloud-point curves for the P(DDMA) in C-4 hydrocarbons are at lower temperatures than the P(DDMA) + C-3 hydrocarbons curves at fixed pressures.