High-pressure phase behavior data were reported for poly(dodecyl acrylate) [P(DDA)] in propane, propylene, butane, 1-butene, and dimethyl ether (DME), as well as for the P(DDA) + dodecyl acrylate (DDA) (or DME) in CO(2). Cloud-point curves for P(DDA) in C(4) hydrocarbons were about 90 K higher than P(DDA) + C(3) hydrocarbon curves, at a fixed pressure of about 10.0 MPa. The cloud-point curve for the P(DDA) + DME mixture was located between C(3) and C(4) hydrocarbons at pressures below about 20.0 MPa. The location of the P(DDA) + CO(2) cloud-point curve shifts to lower temperatures and pressures upon the addition of DDA or DME. High-pressure phase equilibrium data were presented for the CO(2) + DDA system at temperatures ranging from (313.2 to 393.2) K and pressures up to about 26.14 MPa. The CO(2) + DDA system exhibits type I phase behavior with a continuous critical mixture curve and was adequately modeled using the Peng-Robinson equation of state.