Measurement and correlation of phase equilibria for the ternary system dodecane + sec-butylbenzene + N-methyl-2-pyrrolidone (NMP) were carried out over a temperature range of (288.15 to 318.15) K and at atmospheric pressure. Such a system is found in the extraction of aromatics in the production of middle distillate. The system studied exhibits type I liquid-liquid phase diagram. The values of distribution coefficients and selectivities were calculated from the equilibrium data. The effect of temperature and solute concentration in the feed upon solubility, distribution coefficient, and selectivity were investigated experimentally and theoretically. The experimental results of the studied system was regressed to estimate the interaction parameters between each of the three pairs of components with NRTL and UNIQUAC models as a function of temperature. Both models satisfactorily correlate the experimental data; however, the UNIQUAC fit was slightly better than that obtained with the NRTL model.