This Demonstration computes the liquid-liquid equilibrium diagrams of these four mixtures at user-set values of the temperature . For example, for the first ternary mixture the binodal curve and the plait point are shown by a magenta curve and a red dot, respectively (see snapshot 1). All calculations are based on the arc-length continuation technique. Parameters for the NRTL model, used to compute the activity coefficients, were obtained from the process simulator of AspenTech. As shown in the four snapshots, our results obtained at (see the magenta curves) agree perfectly with those given by the Aspen Properties package (indicated by the green squares).