Liquid-liquid equilibrium data of the solubility (binodal) curves and tie-line end compositions are presented for mixtures of [water (1) + formic acid or propanoic acid or levulinic (4-oxopentanoic) acid or valeric (pentanoic) acid or caproic (hexanoic) acid (2) + 1-octanol (3)] at 293.15 K and 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 tertiary associated systems containing proton-donating and -accepting components capable of a physical interaction through hydrogen bonding. The model combines the solvatochromic parameters with the thermodynamic factors derived from the UNIFAC-Dortmund model. The reliability of the model has been analyzed against the LLE data with respect to the distribution ratio and separation factor. The tie-lines were also correlated using the UNIFAC-original model. The proposed model, reflecting the simultaneous impact of hydrogen bonding, solubility and thermodynamic factors, yields a mean error of 27.9% for all the systems considered. (C) 2004 Elsevier B.V. All rights reserved.