The solubilities of carbon dioxide are reported in mixed solvents containing (1.68 to 3.00) kmol/m(3) (N-methyldiethanolamine), (0.36 to 1.36) kmol/m(3) (piperazine), (0.36 to 1.36) kmol/m(3) (tetramethylensulfone or sulfolane), and water for temperatures from (40 to 70) degrees C and CO2 partial pressures in the range of (30 to 3900) kPa. The results show that piperazine has an effect on the CO2 solubility and sulfolane behaves as a physical solvent.