Great significant is attached to phase equilibria in the design and optimization of separation process since it provides quantitative information on compositions in vapor and liquid phases. The objective of this work is to develop a methodology for studying the vapor-(liquid)-liquid phase behavior of ternary systems and for rapidly determining the presences of partial miscibility and ternary azeotrope by using the commercial simulator PROII (Simulation Sciences. 1992), for the phase equilibrium calculation and generation of multiple data. The methodology uses flash simulation to do liquid-(liquid)-vapor equilibrium calculations : simulation results are used to generate equilibrium surfaces, which enable the thermodynamic characterization of ternary systems. Every system has three equilibrium surfaces, y(1), y(2) and y(3). In the equilibrium surfaces one can observe if the system presents a gap of miscibility by observing a flat line formation. The number and extent of the flat lines give the dimensions of partial miscibility region of the system. It is possible also to identify, from the equilibrium surfaces, points for which x(1) = y(1), x(2) = y(2) and x(3) = y(3). Lines formed by these points are designated non-ideality lines (x(1) = y(1) and x(3) = y(3)) and inversion line (x(2) = y(2)), and they are used to verify if there exist ternary azeotropes. In this work we are establishing a relationship between the characteristic shape of the inversion line and the choice of the best solvent or entrainer to separate mixtures by extractive or azeotropic distillation. The developed methodology still can determine three phase equilibrium compositions.