Liquid-liquid equilibria were measured at 20-degrees-C in the W-MeOH-MTBE-EG quaternary system (W is water, MeOH is methyl alcohol, MTBE is methyl tert-butyl ether, and EG is ethylene glycol) and in the W-MeOH-MTBE, W-MTBE-EG and MeOH-MTBE-EG ternary systems. In the W-MeOH-MTBE-EG, W-MeOH-MTBE, and MeOH-MTBE-EG systems, the vapour-liquid equilibria at atmospheric pressure were also measured. The experimental data of the quaternary system were compared with those modelled by superposition of the Wilson and Redlich-Kister equations with the ternary term, whose parameters were determined based on the corresponding binary and, in some cases, ternary systems. A very good agreement was obtained for both the liquid-liquid and vapour-liquid equilibria.