Extraction equilibria of the systems (water + carboxylic acid + 1-hexanol/Alamine 300) have been investigated at T=298.2 K. Among the studied C1-C3 carboxylic acids, propanoic acid gives the largest distribution ratio and separation factors, as compared to formic and acetic acids. The equilibrium data of monocarboxylic acids are used to establish the basis to an analytical structure for optimum extraction. Some aspects of selection of an appropriate criterion for designing optimum extraction are discussed. Solvation energy relation (SERLAS) with five parameters has been performed to estimate the properties of extraction systems containing a protic alcohol solvent. The tie-lines of the present systems have been predicted by the UNIFAC-original model. The reliability analysis of both models has been made statistically against the experimental extraction factors. (C) 2013 Elsevier B.V. All rights reserved.