Tie-line compositions for type 11 systems of 1-methyl-3-octylimidazolium bis[trifluoromethylsulfonyl]imide + thiophene + 2,2,4-trimethylpentane or + toluene have been determined at 298.15 K and atmospheric pressure. Solute distribution coefficient and selectivity values have also been determined. The experimental data were correlated with the NRTL and UNIQUAC equations. The best results were found with the UNIQUAC equation. The NRTL equation could not adequately correlate the system with toluene.