(Liquid + liquid) equilibria and tie lines for the quaternary systems of (water + ethanol + dimethyl carbonate + diethyl carbonate) and (water + dimethyl carbonate + diethyl carbonate + heptane) and the ternary system of (water + dimethyl carbonate + diethyl carbonate) were measured at T = 298.15 K and atmospheric pressure. The experimental ternary and quaternary (liquid + liquid) equilibrium results were correlated with the modified and the extended UNIQUAC models. The average root-mean-square deviations in the two quaternary system correlations obtained by the modified and extended UNIQUAC models were 0.99 % and 1.21 %, respectively.