The isobaric separation of multicomponent mixtures by distillation require reliable vapor-liquid equilibrium data. Since the experimental determination of multicomponent vapor-liquid equilibrium data is laborious and time consuming there is a need to use a predictive method for the liquid phase activity coefficients. The estimated vapor-phase compositions are dependent on the predictive thermodynamic method used. The ternary vapor-liquid equilibrium data for the system, heptane/ methylcyclohexane/ toluene at 101.325 kPa have been chosen to compare the abilities of the three-suffix Margules and the UNIQUAC Equations in the prediction of isobaric ternary vapor-liquid equilibria with parameters estimated from the corresponding binary vapor-liquid equilibria compositions taken from the literature. The predictions with the three-suffix Margules equations was found to be little superior with overall root mean square deviations of ±0.0047 whereas the UNIQUAC equations could predict the ternary vapor compositions with overall root mean square deviations of ± 0.0061.