High-pressure vapor-liquid equilibria for the binary system carbon dioxide-2-methyl-2-propanol were measured at 299.0, 323.2, and 343.2 K. For the ternary system carbon dioxide-2-methyl-2-propanol-water equilibrium compositions were measured at 323.2 K and pressures of 60, 80, 100, and 120 bar. An isothermal three-phase region at 323.2 K and phase equilibria at 60 and 80 bar are also presented. The experimental data were correlated with the Soave-Redlich-Kwong equation of state with the modified Huron-Vidal second-order mixing rule. The model was able to provide good predictions of the phase behavior of all systems considered in this study.