Understanding the Transition to Unleaded Aviation Gasoline: A Primer (2026)
Chapter: What Is the Status of Unleaded Aviation Gasoline?
- encouraging and incentivizing the development and commercial production of unleaded aviation gasoline, the expansion of distribution infrastructure, and its use.
- Research, development, and innovation. This pillar addresses safety and technical issues with using unleaded aviation gasoline in the existing aircraft fleet and future high-performance engines, as well as ensuring effective and timely FAA certification.
- Unleaded fuel evaluation and authorization. Under this pillar, FAA is tasked with testing and evaluating candidate unleaded aviation fuels, identifying at least one such fuel for widespread use, and institutionalizing the Fleet Authorization process for unleaded aviation gasoline.
- Regulation policy and programmatic activities. This pillar encompasses the regulatory development processes underway at EPA and FAA, as well as efforts to provide funding for airport fueling infrastructure necessary to support the use of unleaded aviation gasoline.
The EAGLE website is a comprehensive source of public information regarding all aspects of the transition to unleaded fuel.
The key features of the EAGLE website include:
- Materials from regular stakeholder meetings to provide updates on activities in each of the four pillars.
- A toolkit with guidance for airports transitioning flight school operations to unleaded aviation gasoline.
- Information on the current availability of unleaded aviation gasolines, as well as the specific aircraft for which they have been authorized for use.
- The status of ongoing testing on candidate unleaded aviation gasolines.
- A list of responses to frequently asked questions.
- The latest news related to the transition to unleaded aviation gasoline.
What Is the Status of Unleaded Aviation Gasoline?
Current gasoline-fueled aircraft are powered by a wide variety of engines and can have different requirements for the aviation gasoline that fuels them. Because many gasoline-fueled aircraft engines were specifically designed to use high-octane leaded aviation gasoline, it has been the most widely used fuel for a long period of time. However, the lead content has been reduced over time, and the current commercial fuel, which is authorized for use in all gasoline-powered aircraft, is referred to as 100LL. The specifications for this fuel are prescribed by ASTM International, (formerly the American Society for Testing and Materials), under the standard referred to as ASTM D910. ASTM International standards are voluntary, consensus-based standards developed by technical committees of industry experts. In the
case of ASTM D910, the standard ensures that commercial 100LL aviation gasoline meets the requirements of gasoline-fueled aircraft engines.
As concerns regarding leaded aviation gasoline grew and efforts to transition to unleaded fuels were initiated, several unleaded fuels were, and continue to be, present in the marketplace to a limited degree. These unleaded fuels include non-oxygenated motor gasoline (mogas), as well as 91- and 94- octane unleaded fuels (UL91 and UL94, respectively). Specifications for mogas are set forth in ASTM D4814, while specifications for UL91 and UL94 fuels are set forth in ASTM D7547. At the time of this publication, according to FAA’s Airport Data and Information Portal, 172 airports in the United States are offering mogas, and 36 are offering the UL94 fuel available from Swift Fuels (FAA 2025).
More recently, two 100-octane unleaded fuels have been authorized for certain gasoline-fueled aircraft by the FAA. The first of these was developed by General Aviation Modifications, Inc. (GAMI) and is known as G100UL (GAMI 2024b). According to the EAGLE website and the FAA’s Airport Data and Information Portal, at the time of this publication, this fuel is available at two airports in the United States (EAGLE 2024b, FAA 2025). The second fuel was developed by Swift Fuels and is referred to as 100R (Swift Fuels 2024b). As of early 2025, 100R received FAA authorization for use in Cessna 172R and 172S equipped with Lycoming IO-360-L2A engines. At the time of publication, it is available at three airports in California, including San Carlos Airport (KSQL), Half Moon Bay Airport (KHAF), and Santa Monica Municipal Airport (SMO) (County of San Mateo 2024, NBAA 2024). Additionally, no ASTM standards have been developed to establish specifications for either of these 100-octane unleaded fuels. Also of note is the fact that a third 100-octane unleaded fuel, UL100E, is being developed by LyondellBasell & VP Racing Fuels, though it is still undergoing testing (VP Racing Fuels 2024).
Aircraft using any of these unleaded aviation gasolines must be covered by FAA supplemental type certificates (STCs) unless their original Type Certificate (TC) and Type Certificate Data Sheet (TCDS) already provide for the use of one or more of these specific unleaded fuels. STCs are fuel and aircraft specific and usually need to be purchased from the fuel provider. They also require the aircraft operator to take additional steps prior to using the unleaded fuel in their aircraft. Alternatively, the FAA can approve fuels via the Fleet Authorization process, developed in conjunction with the PAFI, which addresses the necessary testing and performance requirements. An ASTM specification is also required for fuels authorized through the Fleet Authorization process. The UL100E fuel from LyondellBasell & VP Racing Fuels is being developed under PAFI and, if successful, would be authorized through the Fleet Authorization process. Additionally, according to the EAGLE website, Swift may also seek Fleet Authorization for its UL94 and 100R products, which would eliminate the need for STCs (EAGLE 2024a). It should also be noted that STCs are not available for experimental and/or amateur-built aircraft not covered by a TC/TCDS, but they could be covered under the Fleet Authorization process. This would require the FAA to find an unleaded fuel to be equivalent to 100LL through the Fleet Authorization process and experimental and/or amateur-built aircraft owners to use the information generated to determine that the fuel is acceptable following FAA Policy Statement PS-AIR-20-2000 DRAFT (FAA 2022a).
Additionally, apart from mogas, unleaded aviation gasoline may be more expensive than 100LL, at least during the early stages of the transition period when production volumes are lower and multiple fuels may compete in the unleaded market. For example, fuel price data for 100LL and Swift UL94 (offered at the same airport) were collected in July 2024 from Air-
Nav, an online platform that aggregates airport facility details and aviation fuel prices across the United States (AirNav 2024). Prices were compared for the same type of delivery where possible (e.g., self-serve or full-serve). These data are presented in Table 1. As shown, UL94 was generally more expensive than 100LL, by an average of $0.68 per gallon, even though some airports provide fuel price subsidies to UL94.
Table 1. AirNav fuel price comparisons by airport, July 2024.
| Airport Name | State | FAA ID | AirNav Fuel Price | ||
|---|---|---|---|---|---|
| UL94 | 100LL | Difference | |||
| Bob Hope | CA | BUR | $9.48 | $9.05 | $0.43 |
| Hayward Executive | CA | HWD | $8.99 | $7.79 | $1.20 |
| Livermore Municipal | CA | LVK | $7.60 | $5.99 | $1.61 |
| Long Beach | CA | LGB | $7.95 | $7.95 | $0.00 |
| Oxnard | CA | OXR | $6.95 | $6.48 | $0.47 |
| Reid-Hillview | CA | RHV | $7.64 | Not Sold | N/A |
| San Carlos | CA | SQL | No Data | ||
| San Martin | CA | E16 | $7.39 | Not Sold | N/A |
| Santa Monica Municipal | CA | SMO | $7.10 | $8.60 | ($1.50) |
| Van Nuys | CA | VNY | $7.49 | $7.95 | ($0.46) |
| Watsonville Municipal | CA | WVI | $7.45 | $6.25 | $1.20 |
| Whiteman | CA | WHP | No Data | ||
| Centennial | CO | APA | $8.84 | $7.24 | $1.60 |
| DeLand Municipal | FL | DED | $8.25 | $6.65 | $1.60 |
| Naples Municipal | FL | APF | $7.06 | $6.46 | $0.60 |
| Sebring Regional | FL | SEF | $7.80 | $4.98 | $2.82 |
| Marshall County | IL | C75 | $5.99 | $5.59 | $0.40 |
| Rochelle Municipal | IL | RPJ | $6.50 | $6.45 | $0.05 |
| Griffith-Merrillville | IN | 05C | $7.09 | $6.49 | $0.60 |
| Michigan City Municipal | IN | MGC | $6.75 | $5.34 | $1.41 |
| Reese | IN | 712 | $6.88 | $6.94 | ($0.06) |
| Falmouth Airpark | MA | 5B6 | $9.34 | $6.62 | $2.72 |
| Walter J. Koladza | MA | GBR | No Data | $6.60 | No Data |
| Brooks Field | MI | RMY | $6.18 | $5.65 | $0.53 |
| Oscoda/Wurtsmith | MI | OSC | No Data | $5.70 | No Data |
| South St. Paul Municipal | MN | SGS | $5.79 | $5.69 | $0.10 |
| Airport Name | State | FAA ID | AirNav Fuel Price | ||
|---|---|---|---|---|---|
| UL94 | 100LL | Difference | |||
| Stanton Airfield | MN | SYN | No Data | $5.95 | No Data |
| Brown County | OH | GEO | $6.99 | $6.99 | $0.00 |
| Fulton County | OH | USE | $6.19 | $5.49 | $0.70 |
| Smoketown | PA | S37 | $6.30 | $5.95 | $0.35 |
| Waco Regional | TX | ACT | $6.99 | $6.65 | $0.34 |
| Carter | WI | 92C | No Data | ||
| Cumberland Municipal | WI | UBE | $6.50 | $5.75 | $0.75 |
| Gilbert Field | WI | 94C | No Data | ||
| Price County | WI | PBH | No Data | $5.85 | No Data |
| Sauk/Prairie | WI | 91C | $5.85 | $5.65 | $0.20 |
| Waunakee | WI | 6P3 | No Data | $5.65 | No Data |
Source: AirNav 2024.
Finally, another important consideration with respect to unleaded aviation gasolines is their compatibility with 100LL, as the potential for mixing different aviation gasoline types is high. This potential includes both intentional mixing (such as topping off a tank with a different fuel) and inadvertent mixing (such as through misfueling, where the wrong fuel is dispensed into an aircraft). Misfueling can occur due to factors such as incorrect labeling, misunderstanding of approvals, or lack of awareness, and can have serious safety and compliance implications.
Swift UL94, Swift 100R, and GAMI G100UL can be mixed with 100LL in any proportion, according to their producers (Swift Fuels 2024a, GAMI 2024a). However, while GAMI indicates that G100UL can be mixed with UL94 and 100R, provided the fuel is only used in aircraft with appropriate STCs, Swift states that mixing GAMI G100UL with Swift’s UL94 or 100R is “not advisable at this time,” regardless of aircraft type. Therefore, there are at least two significant issues related to potential misfueling associated with unleaded aviation gasoline. The first of these risks is refueling aircraft that require 100-octane fuel with a lower-octane alternative, such as mogas or UL94, which may not meet the performance requirements of the engine. The second is misfueling that results in an unintended mixture of Swift and GAMI unleaded fuels in an aircraft.
To summarize, other than mogas, Swift UL94 is, as of January 2025, the most widely available unleaded aviation gasoline in the United States. It is subject to an industry consensus ASTM specification and can be used with an STC in over 70 percent of the U.S. piston fleet (Swift Fuels 2024a). Both G100UL and Swift 100R are becoming available, and STC coverage for G100UL extends to all certificated gasoline-fueled aircraft in the FAA database (but not gasoline-powered rotorcraft). However, at the time of this publication, no industry consensus ASTM specification exists for either fuel, which could create concerns for some airports
