Liquid-liquid equilibrium data for solubility curves and tie-line end compositions are presented for mixtures of (water + valeric acid or levulinic acid + propylene carbonate or dimethyl phthalate) ternary systems at T = 298.2 K and barometric pressure. The investigated systems display two types of LLE behaviour. The systems consisting levulinic acid show type-1 LLE behaviour, while type-2 behaviour is exhibited by valeric acid aqueous mixtures. Separation of phases was impossible in high valeric acid concentration when propylene carbonate was used as solvent. The evaluation of the solvents' aptitude was conducted using the calculation of distribution coefficients and separation factors. The measured end points were satisfactorily correlated with the NRTL thermodynamic model. For correlation of distribution coefficients and separation factors in the studied mixtures, Kamlet-Taft LSER model was utilized. All the mixtures were fitted with the LSER model, except the distribution coefficients of (water + valeric acid + dimethyl phthalate) system. Average separation factors and distribution coefficients showed that the number of esteric group has direct effect on extraction ability of studied solvents. LSER calculations verified this subject. (C) 2017 Elsevier Ltd.