Vapor-liquid equilibrium (VLE) at 101.3 kPa have been determined for a ternary system (tetrahydofuran + 2-propanol + 2,2,4-trimethylpentane) and its constituent binary systems (tetrahydrofuran + 2-propanol, tetrahydrofuran + 2,2,4-trimethylpentane, and 2-propanol + 2,2,4-trimethylpentane). The activity coefficients of liquid mixtures were calculated from the modified Raoult's law. Thermodynamic consistency tests were performed for all VLE data. The VLE data of the binary mixtures and ternary mixtures were correlated using the Margules, Wilson, NRTL, and UNIQUAC activity-coefficient models. The models with their best-fitted interaction parameters of the binary systems were used to predict the ternary vapor-liquid equilibrium. All VLE data are also used to calculate the reduced excess molar Gibbs free energy g(E)/RTand the deviations in the boiling point Delta T. The calculated quantities of g(E)/RT and Delta AT were fitted to variable-degree polynomials in terms of liquid composition. (c) 2008 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.