Experimental tie line data of one quaternary mixture for water + methanol + diisopropyl ether + toluene system and one constituent ternary mixtures for the water + methanol + diisopropyl ether system were measured at a temperature of 298.15 K and ambient pressure. The experimental ternary and quaternary liquid-liquid equilibrium data were successfully correlated by using a modified UNIQUAC model including multibody interaction parameters in addition to binary ones. The calculated results were further compared with those obtained from the extended UNIQUAC model of Nagata.