The use of renewable biofuels is a necessity today and entails the improvement and optimization of related processes. The work presents new thermodynamic parameters necessary to optimize the operation of internal combustion engines, improve characteristics and predict the properties of biofuels. Based on the obtained liquid-liquid equilibrium (LLE) data, binodal curves and surfaces are constructed for a system containing ethanol, propionic acid, ethyl propionate and water at 293.15 K and 303.15 K and atmospheric pressure, as well as model calculations of vapor-liquid equilibrium (VLE) data were carried out according to literature results on compositions of chemically equilibrium (CE) mixtures. The results of modeling on liquid-phase and vapor-liquid equilibrium using NRTL and UNIFAC models respectively are presented. A comparative analysis of the results under the temperature conditions of this study is given.