Equilibrium tie line data have been determined at (323.15, 348.15, and 373.15) K for the ternary liquid liquid equilibria (LLE) of three alkane + sec-butylbenzene + sulfolane systems, where the alkanes studied are decane, dodecane, and tetradecane. The relative mutual solubility of sec-butylbenzene is higher in decane + sulfolane than in dodecane + sulfolane or tetradecane + sulfolane mixtures. The tie line data were correlated with the UNIQUAC and NRTL models. The calculated values based on the UNIQUAC model were found to be better than those based on the NRTL model; the average root-mean-square deviation between the phase composition obtained from experiment and that from calculation was 0.00385 for UNIQUAC compared to 0.00566 for NRTL. The values of selectivity and distribution coefficients were derived from the equilibrium data.