The Liquid-liquid equilibrium (LLE) data for the mixtures of {sulfolane (1) + a carboxylic acid (2) + pentane (3)) at 303.15K are reported, where a carboxylic acid refers to acetic acid, propanoic acid, butanoic acid, 2-methylpropanoic acid, pentanoic acid and 3-methylbutanoic acid. The shape of the binodal curves show that the solubility of pentane in (sulfolane + a carboxylic acid) is very much dependent on the carbon number and the type of carboxylic acid. The area of the two phase heterogeneous region for the carboxylic mixtures decreases in the order of acetic acid > propanoicacid > 2-methylpropanoic acid butanoic acid > pentanoic acid similar to 3-methylbutanoic acid. Three parameter equations have been fitted to the binodal curve data. The NRTL and UNIQUAC models were used to correlate the experimental data. The NRTL model fitted the experimental data better than the UNIQUAC model with the average mean square deviation of 0.072 mole fraction as compared to 0.359 mole fraction for UNIQUAC model. (C) 2015 Elsevier B.V. All rights reserved.