Chemical equilibrium for the quaternary system propionic acid + ethanol + ethyl propionate + water was experimentally studied at 303.15 and 313.15 K and atmospheric pressure. The chemically equilibrium compositions were determined by gas chromatography and nuclear magnetic resonance analytical methods. It is shown that chemical equilibrium is reached both in homogeneous and heterogeneous area of composition of reactive mixture. The liquid liquid equilibrium data for the surface of chemical equilibrium were obtained. The thermodynamic constants of chemical equilibrium at 303.15 and 313.15 K were determined. (C) 2017 Elsevier B.V. All rights reserved.