The two leading contenders to replace 100LL with an unleaded equivalent, Swift Enterprises Swift Fuel and General Aviation Modification Inc.s G100UL, both say their fuel will cost more than 100LL. But how much more? We took our own run at it based on what weve been able to glean about these fuels from patent filings and information from the two companies. According to its patent filings and published FAA test data, Swift is a binary blend of mesitylene (also known as trimethylbenzene) and isopentane. Mesitylene is a bit of an exotic, used for specialized solvents and industrial processes. Its a terrific octane enhancer, but so rare in industy that no commodity prices are available. One supplier we contacted sells it for $53 a gallon, a price thats obviously unsustainable for fuel use. Isopentane is a low boiling point hydrocarbon thats produced as a light fraction during initial refining. Some refiners break it down for other uses and its also a constituent in cosmetics. According to the FAAs report, Swift Fuel contains 85 percent mesitylene and 15 percent isopentane, although that ratio may vary. GAMIs G100UL is more complex and variable, consisting of a high-grade aviation alkylate thats similar to the base of 100LL avgas before its dosed with lead and aromatics like tolulene. G100 has been blended in a number of variants, one of which includes mesitylene. More promising economically, however, are G100 blends that include various types of xenols, including para-, meta- or ortho-xylene. These materials are cheaper than mesitylene and traded on chemical commodity markets, thus theyre more widely available. Still, pinning down prices is slippery because like all commodities, these materials have dynamic price swings depending on demand for plastics, chemicals, paints and solvents, in which they are used. Although G100UL lacks the motor octane of either Swift Fuel or typical FBO 100LL, 
100-Octane Cost Data: Sharpening the Pencil
The two leading contenders to replace 100LL with an unleaded equivalent, Swift Enterprises Swift Fuel and General Aviation Modification Inc.s G100UL, both say their fuel will cost more than 100LL. But how much more? We took our own run at it based on what weve been able to glean about these fuels from patent filings and information from the two companies. According to its patent filings and published FAA test data, Swift is a binary blend of mesitylene (also known as trimethylbenzene) and isopentane. Mesitylene is a bit of an exotic, used for specialized solvents and industrial processes. Its a terrific octane enhancer, but so rare in industy that no commodity prices are available. One supplier we contacted sells it for $53 a gallon, a price thats obviously unsustainable for fuel use.