Swift Fuels reached another milestone in early March 2026 with the FAA’s expansion of the number of aircraft engines eligible to use its unleaded 100R fuel.
The March 11, 2026, update to the FAA’s Approved Model List for the company’s STC takes the number of approved engines to more than 800.
Swift Fuels, a leader in the quest for an unleaded fuel for general aviation, had its first success in unleaded fuels with its UL94, approved in 2015. The 94-octane unleaded fuel is sold at more than 100 airports across the country. However, it only serves about 65%-70% of the piston fleet — primarily lower-compression engines. The high-performance engines, like the turbocharged Lycoming 540s and Continental 550s, still required the detonation protection of leaded 100LL.
The First Milestone
The first milestone for the new unleaded fuel was in late 2024 when the FAA granted a limited STC for Cessna 172 R and S models equipped with Lycoming IO-360-L2A engines. For 18 months, 100R was essentially a “test-bed” fuel, used by 10 flight schools across the U.S. and Europe.
That changed in September 2025 when ASTM published a production specification for 100R. Since its beginnings, Swift Fuels has always been a proponent of using the ASTM process to approve its fuels. Company officials noted that a global specification was the only way to ensure global distribution and approvals from Original Equipment Manufacturers (OEM).
With the FAA’s expansion of the AML list, the 100R fuel is approved for engines ranging from 65-hp Continentals to the Lycoming 540 series of engines.
The nine-page list includes 840 engines from Continental, Lycoming, Franklin, Pratt & Whitney, and several radial engines.
What This Means for Aircraft Owners
To use the fuel, once it is available at your airport, you’ll need to have an STC. The company is offering a “Forever STC” for $100.
“Whenever Swift Fuels avgas STCs are approved by FAA, registered avgas STC holders will be notified by Swift Fuels — FOREVER,” the company proclaims on its website. “All specified placards, license rights, and FAA-required forms will then be supplied FREE to each FOREVER avgas STC certificate holder. This is how Swift Fuels will manage ‘fleetwide approval’ for our 100-octane unleaded avgas to replace 100LL.”
Swift Fuels CEO Chris D’Acosta has noted that the company is leveraging its existing UL94 infrastructure to roll out 100R. With millions of gallons already delivered through the UL94 program, the strategy is to swap the lower-octane fuel for 100R as approvals continue to roll in.
See the full list of approved engines here.
Swift is one of three companies in the quest to bring unleaded avgas to general aviation by 2030.
G100UL, developed by General Aviation Modifications Inc., was approved in 2022 by STC for “every spark ignition piston engine and every airframe using a spark ignition piston engine in the FAA’s Type Certificate database,” according to GAMI officials.
The third fuel, UL100E, is being developed by LyondellBasell and VP Racing. It received its initial ASTM specification in January 2026. UL100E is the only unleaded fuel candidate still in the FAA’s Piston Aircraft Fuel Initiative (PAFI) program. The PAFI evaluations are expected to be completed by September 2026, according to Lyondell officials.
For more information: SwiftFuelsAvgas.com
It’s 2 to 4 dollars a gallon more in California. University of North Dakota tried it. Ran 300,000 gallons or more through their engines. Gave it up. Was damaging the valve seals. Swift has run one engine up to 400 hours and said it’s ready to go. So it’s just gonna be perfect for destroying our engines.
To clarify;
high compression engines, typically those with 8.5:1 compression and higher need the 100/130 octane.
Turbo-normalized engines , those that only maintain manifold pressure at sea level, 29-30 inches can probably use lower octane fuel, if the compression ratio is in the 7.5:1 range.
Turbo-boosted engines can have manifold pressures of 36 inches or more, which effectively raises the 7.5:1 compression to close to 10:1, requiring the 100/130 octane fuel.
Wow, that didn’t clarify anything. A normally aspirated aircraft engine with 8 1/2 to one compression ratio is not considered high compression and almost all of these engines are approved by STC to operate on 91 octane unleaded auto fuel.
Turbo normalized engines like the Lycoming I0 540 engine on a Aerostar which has an 8 1/2 to one compression ratio, have had problems with detonation while using 100 LL fuel because the turbo charger cause such an increase in the temperature of the air going to the engine it resulted in a destination problem.
Turbo charged engines that run 7 1/2 to 1 compression ratios with boosts of 36 inches can run with lower octane fuels than 100 LL when they are equipped with high efficiency intercoolers that lower the temperature of the air coming from the turbo charger.
Currently Rotex engines with 11 to 1 compression ratios are using 91 octane fuel.
The statement that swift UL94 is primarily use in low compression engines is totally misleading as the vast majority of turbo charged engines in use that require 100 octane fuel normally have a compression ratio of 7.5 to 1 which is a very low compression ratio. Please stop spreading bad information.