Consistent vapour-liquid equilibrium (VLE) data at 101.32 kPa have been determined for the ternary system 1-butanol + methanol + 2-methoxy-2-methylpropane, correlated by means of the Wilson, NRTL, and UNI-QUAC equations, and compared with the results predicted by using the same equations with interaction parameters obtained from data for the relevant binary systems. The predictions deviated only slightly from the experimental data. The Wilson equation provided the most satisfactory prediction. Moreover, deviations were smaller than those obtained when the equilibrium data were predicted using the ASOG-KT and the original and modified UNIFAC group-contribution methods. The results obtained with a commercial simulator (ChemCAD IV) indicate that extractive distillation with l-butanol as entrainer is a feasible method for the separation of 2-methoxy-2-methylpropane (MTBE) and methanol.