The model of ideal solution of self-associates is applied to analyze possible shapes of the liquid surface for ternary eutectic alloys. The interaction parameters of the constituents that can be expressed by means of melting temperatures have found to have much influence upon this shape. A discussion of that feature in comparison with possible differences in crystal structures is presented. Estimations of the liquids surface for the Ag-Bi-Cu and Bi-Cd-Sn ternaries were carried out. Different reasons found to be important for this three-fold surface have been considered.