(Liquid-liquid) equilibrium (LLE) data for the ternary systems of (water+ carboxylic acid (formic, acetic, propionic or butyric acid)+dimethyl maleate) were measured at T=298.2 K and atmospheric pressure. Selectivity values for solvent separation efficiency were derived from the tie-line data. A comparison of the extracting capabilities of the solvent was made with respect to distribution coefficients, separation factors, and solvent-free selectivity bases. The reliability of the data was ascertained from Othmer-Tobias plots. The experimental data were correlated using the UNIQUAC and NRTL (alpha = 0.2) equations, and the binary interaction parameters were reported. The phase diagrams for the ternary mixtures including both the experimental and calculated tie-lines were presented. (c) 2008 Elsevier B.V. All rights reserved.