Purification of 1-pentene and 1-hexene by distillation from Fischer-Tropsch products is hampered by the close-boiling compounds 2-methyl-1-butene, 2-methyl-1-pentene, and 2-ethyl-1-butene. Etherification and double-bond isomerization of these compounds in the presence of the linear alpha-olefin, with little loss of the alpha-olefin, were demonstrated. The focus of this study is on the hexene isomers. The effects of the feed composition, methanol to tertiary olefin ratio, space velocity, temperature, and different sulfonic acid resin catalysts (Amberlyst 15 and 35) were investigated. Blending octane numbers for the ethers in standard petrol and Fischer-Tropsch petrol are given, showing 2-methyl-2-methoxypentane to be a poor fuel additive. Experimental equilibrium data for the reaction network to produce 2-methyl-2-methoxypentane are also presented.