The (liquid + liquid) equilibrium data (LLE) for the extraction of toluene from heptane with different ionic liquids (us) based on the alkylsulfate anion (R-SO(4)) was determined at T = 313.2 K and atmospheric pressure. The effect of more complex R-SO(4) anions on capacity of extraction and selectivity in the liquid-liquid extraction of toluene from heptane was studied. The ternary systems were formed by [heptane + toluene + 1,3-dimethylimidazolium methylsulfate ([mmim][CH(3)SO(4)]), 1-ethyl-3-methylimidazolium hydrogensulfate ([emim][HSO(4)]), 1-ethyl-3-methylimidazolium methylsulfate ([emim][CH(3)SO(4)]), or 1-ethyl-3-methylimidazolium ethylsulfate ([emim][C(2)H(5)SO(4)])}. The degree of quality of the experimental LLE data was ascertained by applying the Othmer-Tobias correlation. The phase diagrams for the ternary systems were plotted, and the tie lines correlated with the NRTL model compare satisfactorily with the experimental data. (C) 2011 Elsevier Ltd. All rights reserved.