The isobaric separation of multicomponent mixtures by distillation reauire reliable vapour- liquid equilibrium data. Therefore, the separation is dependent on the predictive thermodyna- mic method used for estimation of vapour-Iiquid equilibria. The abilities of the NRTL and LEMF equations to predict isobaric binary and ternary vapour-liquid equilibria using only two or more lower heats of mixing data were compared. A ternary and three binary systems compri- sing the ternary were studied. Both equations gave reasonable results fer binary systems with intermolecular interaetions (HE max < 200 cal/g.mol). For physical interaetions about 235 cal/g.mol the NRTL equation was found to be superior in the predietion of ternary VLE data with Standard deviation ranging from 12-17 % whereas the LEMF equation conld predict the ternary vapour phase with in the accuracy of 16-21 %