The liquid-liquid equilibria (LLE) of four ternary systems comprising toluene, heptane, and an ionic liquid with the cation N-butylpyridinium ([bpy]), or 2-methyl-N-butylpyridinium ([2bmpy]), or 3-methyl-N-butylpyridinium ([3bmpy]), or 4-methyl-N-butylpyridinium ([4bmpy]), and the anion bis(trifluoromethylsulfonyl)imide ([Tf2N]) were determined at 313.2 K and atmospheric pressure. The distribution ratios and the separation factor curves from the LLE data were plotted and compared to those for sulfolane. The results show no significant differences in the values of these parameters between [bpy][Tf2N] and [2bmpy][Tf2N]. and between [3bmpy][Tf2N] and [4bmpy][Tf2N]. The experimental LLE data were satisfactorily correlated by means of the thermodynamic NRTL model. (C) 2010 Elsevier B.V. All rights reserved.