The phase equilibria for the ternary system: dodecane + sec-butylbenzene + N,N-dimethylformamide (DMF) was studied over a temperature range of 288-318 K and at atmospheric pressure. Such a system is found ill the extraction of aromatics in the middle distillate production. 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, and they are equally the same. (c) 2005 Elsevier B.V. All rights reserved.