Extraction of xylenes from straight-run naphtha streams, using a suitable solvent, is an important industrial application. This stud, is concerned with the experimental investigation of the LLE of n-heptane + o-xylene + triethylene glycol (TEG) at 293.1, 303.1, 313.1 and 323.1 K. Results from three versions of UNIFAC model, as provided in ASPEN PLUS (a sequential simulator), are compared to the experimental data. These versions, which differ only in the database for the mutual group interaction parameters, are the standard UNIFAC (with group interaction parameters extracted from vapor-liquid-equilibrium (VLE) databank), UNIFAC-LL (with group interaction parameters extracted from liquid-liquid-equilibrium databank), and UNIFAC-DMD (with group interaction parameters extracted from the Dortmund Data bank). The comparison is made in terms of root-mean-square (RMS) and the average-absolute deviations (AAD) in compositions. The performance of UNIFAC and UNIFAC-LL in describing the experimental data has been found comparable and better than that of UNIFAC-DMD.