Tie lines were investigated for two quaternary systems of water + ethanol + diethyl carbonate + methylbenzene or heptane and three related ternary systems of water + diethyl carbonate + ethanol or methylbenzene or heptane at 303.15 K and atmospheric pressure. The raw experimental tie line data were correlated using the modified and extended UNIQUAC activity coefficient models. The reliability of the experimental tie line data was tested with the OthmerTobias equation. Distribution coefficients were calculated from the experimental tie line data to analyze the solubility of components in aqueous and organic phases.