Abstract: A process to increase the octane number of a naphtha boiling range feed stock has been developed. Using a dividing wall column, the feed stock is separated into a light fraction comprising compounds containing five carbon atoms or less, an intermediate fraction containing largely compounds having six carbon atoms, and a heavy fraction which comprises compounds containing more than six carbon atoms. The light and heavy fractions are passes to a gasoline blending pool. The intermediate fraction is isomerized to increase the octane number of the intermediate fraction and form an isomerate. The isomerate is passed to the gasoline bending pool.