This paper investigates high-pressure phase transitions for the binary system carbon dioxide (CO2) + methyl methacrylate (MMA) and for the ternary system CO2 + MMA + poly (dimethylsiloxane) vinyl terminated (PDMS-V). The experiments were carried out using the static-synthetic method in a stainless steel equilibrium cell with a variable-volume, including piston and sapphire window, at temperatures of 323.15, 333.15, 343.15 and 353.15 K and the molar fraction ranging from 0.6949 to 0.9499 and 0.6833 to 0.9444 for the binary and ternary systems, respectively. For the binary system, phase transition was determined from the liquid region to the two-phase region. High miscibility of carbon dioxide in MMA was observed with a significant volumetric expansion of the liquid phase. The surfactant PDMS-V was added to this binary system in order to investigate its effect on the phase behavior. For the ternary system CO2 + MMA + PDMS-V, phase transitions were observed from the liquid homogeneous phase until the two-phase region. The results indicate that the addition of PDMS-V led to a small increase in the phase transition pressure, and for the liquid-liquid region a large increase in the phase transition pressure of the system occurred at all temperatures.