The NRTL and UNIQUAC parameters for ethanol-2-butanol-water and ethanol-water-l-butanol systems are determined from the vapor-liquid equilibrium (VLE) data of the constituent binary mixtures and the vapor-liquid-liquid equilibrium (VLLE) data of the ternary mixtures. Those parameters are used to calculate the isobaric ternary VLLE, and the effect of parameters on the calculated VLLE is discussed. The isobaric ternary VLLE are calculated by the parameters determined from the isobaric VLE data of the constituent binary mixtures, but the binodal curves are quite different from the experimental data. Then, the parameters for VLE and LLE calculations are separately determined using the VLE and LLE data on the ternary binodal curve. The LLE parameters are determined by a newly developed method, where the parameters for partially miscible binary mixture are preliminary determined from the pseudo-binary LLE data that are obtained from the ternary LLE data, and then the rest of LLE parameters of the ternary systems are determined. The isobaric VLLE of ethanol-2-butanol-water and ethanol-water-l-butanol systems are calculated by the parameters determined from the present method, and show good agreement with the experimental data, compared with those by Katayama's method. The proposed method is also successfully applied to ethyl acetate-ethanol-water system. (c) 2005 Elsevier B.V. All rights reserved.