High-pressure VLE and VLLE for both the binary mixtures of the carbon dioxide-3-methyl-1-butanol and carbon dioxide-3-methyl-2-butanol and the ternary mixtures of the carbon dioxide-3-methyl-1-butanol-water, carbon dioxide-3-methyl-2-butanol-water and carbon dioxide-2-methyl-2-butanol-methanol were measured at 313.2 K. The phase equilibrium apparatus used in this work is of the circulation type in which the coexisting phases are recirculated, on-line sampled and analyzed, The critical pressures and corresponding mole fractions at 313.2 K were also carefully determined for two binary mixtures. Two water-containing ternary mixtures showed the liquid-liquid-vapor phase behavior over the range of pressure up to their critical point, while for a methanol-containing ternary mixture only two phases coexist at equilibrium. The binary equilibrium data were all reasonably well correlated with the Redlich-Kwong, Soave-Redlich-Kwong, Peng-Robinson, and Patel-Teja equations of state incorporated with eight different mixing rules; the van der Waals, Panagiotopoulos-Reid, and six modified Huron-Vidal mixing rules with UNIQUAC parameters.