HONDA has investigated On Board Separation (OBS) of high octane alcohol and aromatics from current commercial fuels such as E10, a blend of 10 volume % ethanol and 90 volume% gasoline. The high-octane components concentrated from commercial fuel can be injected when needed to suppress knock. The availability of high octane fuel enables the engine to be designed with compression ratio and boost which gives the Octane Boost Engine (OBE) higher efficiency. 3M has developed pervaporation separation modules made with flexible organic membranes that selectively remove and concentrate ethyl alcohol and methyl alcohol from gasoline blends. The separation module profile can be circular or rectangular to best fit the available space. Organic membrane performance has been studied up to 15% ethyl alcohol and up to 15% methyl alcohol blended with 5% ethyl alcohol added for humid condition stability. Performance stability has been evaluated for hundreds of separation hours. Module and membrane stability against thermal shock and vibration has also been evaluated. Test results show progress toward a commercially viable fuel separation system to boost fuel efficiency.