The Clegg-Pitzer equations, expressed on a mole fraction basis, comprise an extended Debye-Huckel term which is a function of composition and a Margules expansion carried out to the three-suffix level, with some simplifications are used to correlate and predict the vapor-liquid equilibrium data for the CO2-Mixed amine aqueous system. The interaction parameters determined from data for the binary and ternary (single amine) systems can be used to predict the quaternary mixed amine system without any additional parameters. The model is applied to the CO2-MDEA-MEA-H2O system containing three neutral solvents (MDEA, MEA, and H2O) and four ionic species (MDEAH+, MEAH+, HCO3-, and RNHCOO-) with four chemical equilibria simultaneously involved.