The liquid-liquid equilibrium for the quaternary system toluene + water + propionic acid + ethyl acetate was measured at 25 degrees C and atmospheric pressure. Binodal curves, tie lines, a distribution curve, and a selectivity curve for the quaternary system have been determined in order to investigate the effect of using binary solvents toluene and ethyl acetate on extracting propionic acid from aqueous solution. In addition, these experimental tie-line data were also compared with the values predicted by the UNIFAC model. It was shown that the UNIFAC model was capable of predicting the compositions of these quaternary systems within an average rmsd of 3.21 mol %.