The phase behavior of six ternary systems involving an aromatic hydrocarbon (benzene, toluene or m-xylene), an aliphatic hydrocarbon (nonane or undecane), and an ionic liquid (1-octyl-3-methylimidazolium hexafluorophosphate, [omim][PF6]) was experimentally studied at 298.15 K and atmospheric pressure, totalizing 26 tie-lines. The main goal is to determine if [omim][PF6] is a good solvent for the separation of the aromatic and aliphatic compounds, a common operation in the processing of reformed naphtha. All the ternary diagrams are of type 1, with high and wide two-phase regions, which show that [omim][PF6] is a good solvent for the extraction of aromatic from aliphatic hydrocarbons. The Othmer-Tobias correlation was used for evaluation of the quality of the tie-line data, with good results. The data were correlated with the NRTL model for the activity coefficient, with estimation of new interaction energy parameters by using a modified Simplex method and a composition-based objective function. The results, expressed by root mean square deviations between experimental and calculated compositions, are very satisfactory. (C) 2010 Elsevier B.V. All rights reserved.