Isobaric vapor-liquid equilibrium (VLE) data were measured for the binary systems propan-l-ol + propanoic acid, propan-l-ol + propyl propanoate, propyl propanoate + propanoic acid, and water + propyl propanoate at 101.3 kPa. Isothermal liquid-liquid equilibrium (LLE) data were measured for the ternary system propan-l-ol + water + propyl propanoate at 288.15 K. VLE and LLE data were fitted using the UNIQUAC model to account for non idealities in the liquid phase while the Hayden O'Connell equation of state was used to account for nonidealities in the vapor phase. The models are in good agreement with the experimental data. The UNIQUAC parameters obtained from the data regression can be used to effectively describe the thermodynamic behavior of the quaternary mixture in a reactive distillation process.