The NAS study was directed by Congress to ignore all of the current Unleaded fuels under development. That is in part why it wallows around in half-baked options… Both the GAMI and Swift UL100 fuels are “Drop-in” replacements with viable formulas able to be produced in existing refineries with existing processes and additives. They are languishing in part because they are designed around a proprietary license model, and haven’t been developed by the producers… The Shell product had issues with dissolving paint, and the Phillips product (“About 5 years away…”) uses Manganese salts and scavengers that also have health risks… GAMI and Swift fuels have been delayed by indecision over testing methodology and criteria for actually granting approval for these fuels… The few refiners brewing 100LL aren’t going to change over until either ordered to by the federal government or forced to by cutoff of Tetraethyl lead supply from Innospec. Most medium to small airports can’t afford to add new tanks, so adoption of UL94 requires arm-twisting to get one of existing tanks/refueling operators to switch… And it requires distribution infrastructure (transport/storage/deliveries) to mitigate the cost premium away from the Indiana refinery now producing it…