A selective alkene upgrading process wherein a mixture of intermediate molecular weight monoalkenes comprising at least one linear alkene component and at least one tertiary alkene component is contacted under selective olefin interconversion conditions with medium pore, shape selective acid catalyst, such as MCM-22 aluminosilicate zeolite, thereby converting at a major amount of linear intermediate alkene to lower alkene while leaving tertiary alkene substantially unconverted. In the preferred embodiments, the process interconversion conditions comprise reaction temperature in the range of about 300.degree. C. to 550.degree. C., pressure in the range of 100 kpa to 1000 kPa, thereby selectively converting at least 60% (net) of linear intermediate alkene while converting less than 20% (net) of branched alkene. By etherifying at least a portion of the unconverted tertiary alkene, an oxygenated fuel having enhanced octane rating is obtained. Cracked lower olefins may be recovered for upgrading.