The purification of I-hexene from Fischer-Tropsch products requires the removal of the close-boiling isomers 2-methyl-1-pentene (2M1P) and 2-ethyl-l-butene (2E1B), by double bond isomerization and etherification with methanol. These reactions were found to be inhibited by oxygenates. The contribution of heavier alcohols, carbonyls, carboxylic acids, and esters were investigated at a methanol-to-tertiary olefin molar ratio of 2.5:1 and 70 degrees C over an acidic resin catalyst (Amberlyst 15). All oxygenate classes caused a decrease in etherification selectivity, either by reducing the activity coefficient of methanol or via side reactions that shifted the etherification equilibrium. Side reactions likely to produce water were expected to suppress conversion, but the extent of such reactions in the present investigation was insufficient to result in a decrease in conversion, except in the case of carboxylic acids.