Liquid-liquid equilibria of ETBE-EtOH-H2O mixtures are measured at 15, 25 and 35 degrees C. UNIQUAC and NRTL equations are fitted to the experimental data using ASPEN PLUS. Both the experimental and correlated values of the equilibrium compositions are compared with the values predicted by UNIFAC method. The same procedure is extended to quaternary ETBE-EtOH-H2O-TBA system at low TBA concentration.