Pervaporation separation and swelling experiments of methanol/methyl tert-butyl ether mixtures were performed by using a flat-sheet, dense poly(2,6-dimethyl-1,4-phenylene oxide) membrane prepared from a chloroform casting solvent. The effect of the feed composition on the membrane performance was described by the permeability of the components, the separation factor, and the sorption selectivity. The effect of the feed temperature on the separation was also studied, and the Arrhenius activation energy for permeability was determined over the whole range of feed composition. Pervaporation operations offered a maximum methanol selectivity of 5.4 and an overall normalized flux of 110 kg(.)mum/m(2)-h. Pervaporation and sorption experiments were also conducted using ethanol, propanol, butanol, and octanol to study the effect of the size of the alcohol molecule on the transport across the membrane.