Extraction of toluene from heptane using binary mixtures of the ionic liquids 1-butyl-4-methylimidazolium tetrafluoroborate [bmim]BF(4) and 1-methyl-3-octylimidazolium tetrafluoroborate [omim]BF(4) have been investigated at 313 K and atmospheric pressure. On the basis of the experimental liquid-liquid equilibrium data, the values of distribution ratio and selectivity for the binary mixtures of the ionic liquids were calculated and compared to those of the pure ionic liquids and sulfolane. None of these two pure ionic liquids showed simultaneously values of distribution ratio and selectivity greater than those of sulfolane. However, our results show that the use of binary mixtures of ([bmim]BF(4) + [omim]BF(4)) has a synergistic effect on toluene extraction. Both the distribution ratio and selectivity are improved with respect to those predicted by an ideal mixing. As a result, it was found that a mixed ionic liquid solvent with a composition of 80 molar % [bmim]BF(4) presents values of selectivity and distribution ratio nearly equal to those of sulfolane.