Tie-fine data for ternary systems including methanol (CH3OH), water (H2O), benzene (C6H6), and cyclohexane (C6H12) were investigated. Phase diagrams of {w(1) H2O + w(2) CH3OH + (1 - w(1) - w(2)) C6H12}, {w(1) H2O + w(2) C6H12 + (1 - w(1) - w(2)) C6H6}, and {w(1) CH3OH + w(2) C6H6 + (1 - w(1) - w(2)) C6H12}, where w is the mass fraction, were obtained at T = 303.15 K. A quaternary system containing these four compounds {w(1) CH3OH + w(2) C6H6 + w(3) C6H12 + (1 - w(1) - w(2) - w(3)) H2O} was also studied at the same temperature, while the system {w(1) H2O + w(2) CH3OH + (1 - w(1) - w(2)) C6H6} was taken from the literature. 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 CH3OH drawn into the aqueous phase. On the other hand, the results also show that the aqueous phase generally contains a higher concentration of C6H6 compared with C6H12. The ternary experimental results were correlated with the UNIQUAC equation, and predicted with the UNIFAC group contribution method. The equilibrium data of the four ternary systems (including that taken from the literature) were used to determine interaction parameters for the UNIQUAC equation. These parameters were then used to predict equilibrium data of this quaternary system. The UNIFAC method was also used with the same purpose. The UNI-QUAC equation appear to be more accurate than the UNIFAC method, particularly for the {w(1) CH3OH + w(2) C6H6 + (1 - w(1) - w(2)) C6H12} ternary system, because it predicts an immiscibility region much larger than the experimentally observed. However, both models have small and similar deviations between experimental and predicted values for the quaternary system. (C) 2003 Elsevier Science Ltd. All rights reserved.