Vapor-liquid equilibrium data for carbon dioxide + methyl methacrylate are reported at temperatures of 308, 313, 323, and 333 K and pressures in the range of 1-8 MPa. The corresponding measurements of the volumetric expansion of the liquid phase are also presented. A linear relationship is observed between pressure and liquid-phase composition for all of the temperatures considered. The Peng-Robinson equation of state provides a satisfactory correlation of the vapor-liquid equilibrium data. It is also shown that the expansion isotherms coincide when plotted as a function of the liquid-phase composition. The high solubility of carbon dioxide in methyl methacrylate and the significant volumetric expansion of the liquid phase indicate that methyl methacrylate is an appropriate choice for investigating the concept of polymerization in monomers expanded with carbon dioxide.