Liquid-liquid equilibrium (LLE) data for ternary systems formed by aromatic compounds (benzene, ethylbenzene), cycloalkanes (cyclohexane, methylcyclohexane, cyclooctane), and the ionic liquid 1-butyl3-methylimidazolium methylsulfate, [BMim][MSO4], have been measured at T = 298.15 K and atmospheric pressure, with the aim of studying the influence of the structure of cycloalkanes and aromatic compounds on liquid-liquid equilibrium. Values of solute distribution ratio and selectivity were evaluated to check the ability of [BMim][MSO4] as a solvent for extraction. The results obtained were compared to those previously reported using other ionic liquids and sulfolane. The nonrandom two-liquid (NRTL) and universal quasichemical (UNIQUAC) thermodynamic models were used to correlate the experimental LLE data for all of the studied ternary systems.