Thermodynamic laws are usually given in forms containing ordinary or partial derivatives of functions that are given in measured data tables. A principal problem is the approximation of these functions and their derivatives. Comonotonic approximation of binary Vapour Liquid Equilibrium data has been leading us to a special two dimensional surface. A special analogy of thermodynamic or mathematical surfaces over two-dimensional basic simplexes is discussed that gives possibility to construct a new type of minimal energy surfaces. Isothermal and isobaric ternary Vapour Liquid Equilibrium data are tested by the new minimal energy surfaces. Pressure-volume-temperature data together with Speed of Sound data are investigated, too.