Tie-line data for the water, ethanol, and cyclohexane [{w(1)H(2)O +w(2)C(2)OH+ (1 -w(1) - w(2))C6H12}] ternary system, where w is the mass fraction, was investigated at T = 303.15 K. A quaternary system containing these three compounds and benzene {w(1)C(2)H(5)OH + w(2)C(6)H(6) + w(3)C(6)H(12) + (1 - w(1) - w(2) - w(3))H2O} was also studied at the same temperature, while data on its other two partially miscible ternary systems were taken from the literature [the fourth {w(1)C(2)H(5)OH + w(2)C(6)H(6) + (1 - w(1) - w(2)}C6H12) is not partially miscible]. From our experimental results we conclude that this quaternary system presents a very small water tolerance and that phase separation could produce a considerable loss Of C2H5OH drawn into the aqueous phase. On the other hand, the results also show that the aqueous phase generally contains a higher concentration of C6H6 than of C6H12. A comparison with other similar quaternary systems investigated in our laboratory was also made. The ternary experimental results were correlated with the UNIQUAC equation, and predicted with the UNIFAC group contribution method. As previously, the equilibrium data of the three ternary systems (including those taken from the literature) were used to determine interaction parameters for the UNIQUAC equation. These parameters were then averaged in order to predict equilibrium data of this quaternary system. The UNIFAC method was also used with the same purpose. The UNIQUAC equation appears to be more accurate than the UNIFAC method for this ternary system. However, this last model is slightly better for the quaternary system, as can be seen from the values of both residuals. (C) 2003 Elsevier Ltd. All rights reserved.