Liquid-liquid equilibrium data for the ternary system water-ethanol-diethyl succinate were measured at 303.15 K and 313.15 K and atmospheric pressure. The reliability of the LLE data was confirmed using the Othmer-Tobias correlation. P-x data for the vapor-liquid equilibrium for the binary system ethanol-diethyl succinate at 323.15 K and ethanol + water at 101.3 kPa were also measured. Data were fitted using the modified UNIQUAC and NRTL equations for the liquid phase and the Hayden-O'Connell (HOC) equation for the vapor phase. The models agree reasonably well with the experimental data and can predict reported azeotropic conditions. The NRTL-HOC is capable of fitting the LLE data better than the UNIQUAC-HOC. (C) 2009 Elsevier B.V. All rights reserved.