(Liquid + liquid) equilibrium data of the solubility (binodal) curves and tic-line end compositions are presented for mixtures of [water (1) + acetic acid, or pyruvic (2-oxopropanoic) acid, or tetrahydrofurfuryl alcohol (2) + 1-hexanol (3)] at T = 293.15 K and P = (101.3 +/- 0.7) kPa. A log-basis approach SERLAS (solvation energy relation for liquid associated system) has been proposed to estimate the properties and (liquid + liquid) equilibria (LLE) of associated systems containing proton-donating and -accepting components capable of a physical interaction through hydrogen bonding. The tie-lines were also correlated using the UNIFAC-original model. The reliability of the models has been analysed against the LLE data with respect to the distribution ratio and separation factor. The proposed model appears to be an improvement in data fit for the ternary systems yielding a mean error of 7.25% for all the systems considered. (C) 2004 Elsevier Ltd. All rights reserved.