Isobaric (101.32 kPa) liquic-vapour equilibrium data for the system 1-butanol + ethanol + 2-methoxy-2-methylpropane (MTBE) were determined and fitted with Wilson, NRTL and UNIQUAC equations, and their prediction by various group contribution methods (ASOG and modified and unmodified UNIFAC methods) was examined. The NRTL equation was used to calculate, by simulation, the influence of plate number and entrainer/feed flow ratio on the quantity and composition of the distillate afforded by extractive distillation of azeotropic MTBE + ethanol using 1-butanol as the entrainer. The quantity of distillate and its MTBE content both increased with plate number, and the quantity of distillate also increased with entrainer/feed flow rate ratio.