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Unleaded Avgas

With a focus on innovation, Avfuel Technology Initiatives Corporation (ATIC) is leading the mission to further industry advancements, including bringing unleaded avgas to market. Toward this effort, ATIC is proud to collaborate with General Aviation Modifications, Inc., (GAMI) by providing its distribution expertise for the engineering company’s high-octane unleaded avgas: G100ULTM.

In July 2021, the FAA approved Supplemental Type Certificates (STCs) authorizing use of G100UL high-octane unleaded avgas. GAMI elected to follow the well-established FAA Approved Model List (AML) STC process whereby the FAA issues the initial STCs with an AML of specific aircraft and engines, and then progressively expands the scope of that AML based on additional testing and data. 

As the Approved Model List for these STCs expands over the next several quarters, it will provide the functional equivalent of a fleet-wide certification for spark ignition piston powered aircraft and engines to operate on G100UL avgas. 

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Press Conference    |    GAMI TALKS WITH AOPA    |    GAMI Interview    |    G100UL Details

"We owe it to our industry, our communities and the companies that have worked diligently toward an answer to help make a solution work. Avfuel is honored to provide its expertise to help further the unleaded avgas initiative.”

Craig Sincock, Avfuel President & CEO

Prop Plane

Unleaded Avgas Frequently Asked Questions


G100UL Avgas vs. 100LL

What changes will I have to make to my engine and/or airframe to use G100UL avgas?

No mechanical modifications are required. STC placards will be placed on the engine, STC appliques will be applied to refueling ports, and a simple addition to the POH will be made according to supplied simple instructions.

How much more than 100LL is G100UL avgas going to cost?

Current best estimates are that G100UL avgas will cost 60-85 cents/gallon more than 100LL as the fuel leaves the producer’s facility and begins to enter the stream of commerce. Estimates are based on crude oil pricing at 40-60 dollars/barrel and will vary with the price of crude oil.


How soon can I buy a tank of G100UL avgas at my airport?

Production and distribution will be ramped up as rapidly as possible. It will not happen overnight. See the following section on distribution and availability for further information on the progressive rollout of G100UL.


About G100UL Avgas

What is the octane of G100UL avgas?

During FAA approved detonation testing, the detonation protection from use of G100UL avgas exceeded that of a corresponding ASTM D910 100LL. That detonation testing was personally observed by highly experienced FAA propulsion engineers. 

Other than being lead-free, are there other benefits to G100UL avgas?

It is likely that spark plug maintenance and replacement intervals will be measurably improved in the absence of metallic lead deposits. It is also likely that, over time, an available synthetic oil may double the interval between required oil changes.


What, if any, are the operating limitations/concerns/exclusions with use of G100UL avgas?

There are no known operating imitations, concerns or exclusions. G100UL avgas performs just as avgas 100LL. The engine, aircraft and pilot will not notice an operating difference when utilizing G100UL.


Will the operation of my engine change with G100UL avgas?

It is likely that no change will be detectable to a pilot operating an aircraft, even with sophisticated engine monitors.


Are there any airspeed or range changes or limitations with the use of G100UL avgas?

There are no significant airspeed or range effects with the use of G100UL avgas. The slightly higher density of G100UL (~6.3 lbs/gal) vs. 100LL (~6.0 lbs/gal) is offset by slightly higher volumetric energy density.  As a result, when operating at the same volumetric (GPH) fuel flow, Lean of Peak (LOP), the aircraft may be one or two knots faster.


What is the color of G100UL avgas?

G100UL typically has an orange or amber color.  When mixed in a 50% ratio with blue 100LL, the color is green (similar to the color of earlier 100/130 “green” avgas).


My airplane has a MoGas STC.  Can I mix G100UL avgas with MoGas?

Comingling of G100UL avgas and other gasolines approved for use in your aircraft is specifically authorized in the limitations section of the STC.


Over the past three or four years, I have heard rumors about problems with other candidate unleaded fuels. Those problems are purported to include cold weather starting problems, paint stripping from spillage at the filler for the gas tank, and metal additives that foul spark plugs.  Has GAMI addressed and avoided all of those issues?

All such concerns have been addressed and thoroughly tested. Cold weather operational starting and flight-testing have been conducted extensively, including by an FAA test pilot.

GAMI has completed a highly successful 150-hour engine durability test conducted on an engine that already had 400+ hours of operation on 100LL.  The post-test engine tear-down demonstrated the engine and combustion chambers were noticeably cleaner at the end of that 150 hours operating on G100UL avgas than before the test started.


Are there any known material compatibility issues in aircraft, engines, storage tanks or transportation systems?

Following extensive testing, no compatibility issues have been identified in any aircraft, engines, storage tanks or transportation systems. G100UL is a drop-in fuel, ready to be used within the industry’s existing infrastructure.


Prop Plane


What is an AML STC?

An Approved Model List (AML) STC is a well-established FAA method to provide an orderly process for the expansion of the applicable makes and models of aircraft and engines to any expansion or modification of the original certification basis. Once an initial STC is issued, the AML list attached to the STC will include only a few aircraft and engines. The FAA process simplifies the addition of further makes and models to the AML, because only the STC attachment need be changed as further approved makes and models are added.


Which engines and airframes are covered with the initial STC?

According to a carefully-planned agreement with the FAA, a small number of Lycoming engines and Cessna airframes have been selected for the initial Approved Model List. That list is designed as a “place holder” list for a much larger spectrum of Lycoming and Continental engines that will be added as the AML expands over the next six to 12 months.


Why were those particular airframes and engines selected to be on the initial “Approved Model List”?

Those particular makes and models were selected for a number of reasons.  Importantly, those models encompass a group of engines and aircraft that are commonly used at one or more prominent high-volume flight training schools.

In 2013-2014, Embry Riddle Aeronautical University (ERAU) conducted a successful 150-hour formal FAA-approved and supervised endurance test using G100UL avgas. ERAU has more experience with G100UL avgas than any other entity outside of GAMI. ERAU has also conducted unleaded avgas testing for a number of the PAFI candidate fuels.

In addition, those engine models are generally of lower compression and power, and were a natural first step to the certification of high compression and power engines.


When will the list of approved aircraft and engines be expanded to include the highest performance general aviation aircraft and engines?

The critical 14 CFR 33.37 detonation testing necessary to cover all high horsepower/high compression ratio/turbocharged engines has already been successfully completed and approved by the FAA as of March 7, 2021. Complete Part 23 flight-testing for both a Lycoming powered aircraft and a Continental powered aircraft have been completed and approved by the FAA.  A complete 14 CFR 33.49 FAA certification endurance test has been successfully completed on a Lycoming high-compression turbocharged engine.

The FAA has asked GAMI to conduct two further tests, both of which are now underway. These are routine tests that GAMI has successfully conducted on several previous STC projects. Completion of those two tests should mark the end of all of the testing required to support an expanded Approved Model List. 

At this time, GAMI knows of no general aviation aircraft or engine that does not fall within the scope of that planned expansion of the Approved Model List. The scope of that expansion plan has already been coordinated with the FAA and is part of the approved certification documents.


What will the STC cost?

The STC pricing will be reasonably based on engines and horsepower in a manner similar to the pricing for other fuel STCs that have been available for low octane gasolines. 


What is included in the STC paperwork?

A short Approved Flight Manual Supplement (AFMS), placards to be installed around the fuel filler ports on the aircraft, a placard to be affixed to the engine and any appropriate instructions. 

When may we anticipate a fleet-wide approval for G100UL? 

All the most difficult tasks required to certify G100UL avgas for a functional fleet-wide expansion of the approved model list have been completed and formally approved by the FAA.

These include hot day/hot fuel flight testing of a high-compression turbocharged aircraft to 25,000 feet, a 150-hour endurance test and extensive material compatibility testing. An expanded AML list will be the “surrogate” for what is commonly referred to as a functional fleet-wide approval. That is planned to occur within the next few calendar quarters.


Will any aircraft/engines be excluded?

GAMI does not anticipate that any piston aircraft or engine that is generally considered part of the general aviation fleet will be excluded. 


Will G100UL avgas be approved for “Warbirds” at full rated power?

It is anticipated that G100UL will be approved for “Warbird” operation under the same limitations, if any, as are appropriate for operation with 100LL.

However, detonation testing data supports a “full rated power” application. The standard ASTM detonation test for operation at full take-off power (D909) demonstrates G100UL is superior even to the old 115/145 “purple” avgas used on DC-7s and Constellations.


Prop Plane

Testing and Approval


Is G100UL avgas approved by the FAA?

The initial STCs with the initial Approved Model Lists have been signed and approved by the FAA. There is one STC for an initial group of aircraft and a separate STC for their corresponding engines. FAA was on-site in the GAMI test cell in Ada simultaneously observing engine runs remotely through four test stand computers.


Did GAMI engage any subject matter experts to assist with the technical issues that were identified during the development of G100UL avgas? 

Yes. GAMI has had extensive technical support from one of the world’s premier specialty chemical companies, which provided substantial technical assistance with the development of the test protocols for assuring the production quality control of G100UL. In addition, at various times, GAMI sought out and obtained technical assistance by three former refining industry employees with specific, long-term experience in relevant areas.

At various times, combinations of 12 senior FAA engineers and program managers have been on site in Ada and other locations to personally observe flight testing, engine durability, post-test engine tear down inspections, material compatibility testing, flight testing and back-to-back engine detonation testing of G100UL vs 100LL.


Were there any new or novel discoveries or innovations that led to the successful approval of G100UL avgas?

There were several significant break-through discoveries in the 2012-2014 timeframe. 

In the fall of 2015, after an extensive, year-long internal technical review, the results and applicability of two of those discoveries to the certification of engines for operation on unleaded aviation gasoline were formally approved by the FAA Engine Propeller Directorate in a formal G100UL project issue paper. 


What specific tests were conducted?

The list of tests conducted is comprehensive and extensive.  Among those: 

  • Material compatibility testing was identified as an early go/no-go requirement that took nearly a year to complete.
  • Hot day, hot fuel, high-altitude and engine restart tests were completed early in the process.
  • Thorough detonation testing has been conducted, as noted below. 


Detonation testing has always been considered the main problem. Were the detonation test plans and testing approved by the FAA?

The means and methods for detonation testing were thoroughly scrutinized, reviewed and approved by the FAA. As far as GAMI is aware, GAMI now has the only modern, internal cylinder pressure sensor based aircraft engine detonation test methodology that is specifically approved by the FAA through its highest-level formal issue paper process.


What was the compression ratio, manifold pressure and the highest horsepower achieved during detonation testing that successfully passed a formal FAA 14 CFR Part 33.47 detonation test?

At the conclusion of the two days of detonation testing, GAMI elected to complete an optional test item from the FAA-approved test matrix.

That test item was to determine the maximum Brake Horsepower (BHP) at which the 8.7:1 CR IO-550 turbocharged test engine could be operated and continue to pass a standard Part 33.47 FAA detonation test.

With redline cylinder and induction air temperatures, the engine operated at 41.4” MP, 380 actual BHP (414 BHP when corrected to standard day conditions). We were unable to determine how much more additional HP could be obtained because the pressure relief “pop-off” valve on the induction system was limiting further increases in manifold pressure.


What additional testing is planned/necessary?

With the concurrence of the FAA, there are only two additional tests required before GAMI will seek FAA approval to expand the AML STC. As mentioned above, those are routine tests that GAMI has previously successfully conducted in connection with previous STC projects. Final preparation of that testing is now underway. 


Have the aircraft and engine original equipment manufacturers (OEMs) been involved in the development?

Early in the development of G100UL avgas, both Lycoming and Continental sent engineers to GAMI in Ada who evaluated G100UL avgas and flew a turbocharged Cirrus operating on G100UL avgas in one wing tank and 100LL in the other. There were no concerns or objections raised by either OEM engine manufacturer to the observed performance of the G100UL avgas. 

In addition, Cirrus Aircraft had one of their senior managers come to Ada. He was an experienced pilot who also flew with G100UL avgas in a Cirrus aircraft to evaluate its performance against 100LL.

In addition, Cirrus conducted extensive material compatibility testing of G100UL avgas with its composite fuel tank materials using its FAA approved testing protocols.


Have any of the aviation organizations had any direct involvement?

At a critical time in the G100UL avgas project, many organizations have provided technical support.


Does G100UL avgas have an ASTM specification?

GAMI has elected to use the already-approved STC path to an FAA approval of the engines and aircraft in the fleet to operate on a new fuel chemistry; no separate ASTM specification is required. 


Why did GAMI elect to pursue the STC certification path rather than join the FAA Piston Aviation Fuel Initiative (PAFI)?

Primarily because the PAFI process began three years after GAMI had initiated the G100UL avgas STC project and there was no mechanism within the PAFI project for GAMI to obtain credit for the substantial certification work the FAA had already approved. 


Are there any new toxicity concerns with G100UL compared to 100LL?

The components in this new high-octane unleaded avgas have been carefully vetted and no new toxicity issues have been found. A draft Material Safety Data Sheet (MSDS) has been developed in consultation with world-class experts in that field. That new MSDS is consistent with existing MSDS documents for other transportation gasolines widely used in the marketplace.


Distribution and Availability

GAMI is a small company. How is GAMI going to create the infrastructure and finance the inventory to produce millions of gallons of G100UL avgas?

GAMI has partnered with Avfuel Corporation through Avfuel Technology Initiatives Corporation to oversee the logistics and distribution. Avfuel is a global supplier of aviation fuels and services, and currently sells 100LL to more than 650 FBOs.  


Are there any concerns regarding price or availability given the proprietary formulation of G100UL and competitive nature of high-octane unleaded avgas?

Avfuel Technology Initiatives Corporation (ATIC) and GAMI have put in place specific contractual language that allows any legitimate distributor and supplier of G100UL avgas non-discriminatory pricing and access to all available supplies. 

GAMI and ATIC believe the contract and licensing terms of the G100UL avgas producers, blenders and distributors will result in the elimination of some existing transportation-cost-related market inefficiencies arising out of existing proprietary sourcing and distribution of 100LL. 


What airports will be the first to have G100UL avgas?

Most likely, the first airport to have G100UL avgas will be co-located with one of the large flight training schools.


How long will it take in order for G100UL avgas to be widely or routinely available?

It is anticipated that the availability of G100UL avgas will expand nationally over a period of a few years at a pace determined by eventual depletion of 100LL stocks, the number and location of new producers and blenders, and the mandates of federal and local governments.


Will there be specific FBOs that will be unable to get access to supplies of G100UL avgas due to proprietary licensing to certain suppliers and vendors?

No such limitations are expected. Avfuel Technology Initiatives Corporation and GAMI have committed that the logistics and licensing of distribution will ensure that G100UL is fairly accessible and priced.   


I fly from airports in Northern California. I am concerned 100LL will be banned before G100UL is widely available. Will there be any priority for airport locations in regions of the country that have a history of high-profile environmental activity?

While that is a concern, it is unlikely that any significant number of municipalities will ban 100LL in the absence of an alternative. Avfuel Technology Initiatives Corporation and GAMI are aware of that potential issue and are actively working to mitigate that possibility.


Will multiple high-octane avgas fuel alternatives exist in the marketplace?

That outcome is very unlikely. While G100UL is approved to be miscible in any proportion with any currently certified aviation gasoline, neither G100UL nor any other candidate unleaded fuel is approved to be miscible with one another.

Because avgas volumes are low relative to jet fuel, and because airport fuel storage tanks have become very expensive to construct and maintain, it is unlikely that any given airport or FBO will have multiple unleaded fuels for sale.

Nor is it likely that different FBOs will carry other formulations of unleaded avgas. That situation would create a significant safety concern whereby an aircraft certified on one fuel might pump another fuel for which it is neither certified nor miscible.


Avfuel Avgas Refueler Truck

History of Unleaded Avgas Initiative

The initiative to develop G100UL avgas was prompted by growing environmental interest in removing the last vestiges of lead from 100LL avgas—the only commercially-available motor fuel to still contain lead. 

Finding a commercially viable unleaded avgas solution was not only important to the industry from an environmental standpoint, but also because spark ignition piston powered aircraft that require avgas are responsible for a number of high-value operations for the aviation industry, as well as local and state communities. These critical infrastructure activities include:

 • Pilot training essential to all aviation segments  • Small businesses requiring flexible connectivity 
 • Medical air transport  • Pipeline inspections that require small aircraft 
 • Search and rescue  • Access to remote communities
 • Firefighting via helicopters and other small aircraft  • Law enforcement
 • Agricultural applications, such as crop spraying  • Border patrol

About GAMI

General Aviation Modifications, Inc. (GAMI), is an innovative general aviation engineering company established in 1995 by Tim Roehl and George Braly. GAMI’s first FAA-approved product was the widely-adopted GAMIjector® fuel injectors, which were awarded the 1996 Aviation Consumer Product of the Year. 

Following the success of the GAMIjector fuel injectors, GAMI created the most sophisticated aircraft piston-engine test facility in the country, which the company has used to support multiple FAA type certificate projects and the development of turbonormalizing systems now installed in more than 2,000 high-performance Bonanza, Cirrus and Cessna aircraft.  For more information, visit and   

Avfuel’s Sustainability Efforts


Supporting industry development is important to Avfuel, which is why it created Avfuel Technology Initiatives Corporation. Founded in January of 2012, the company’s mission is to further industry advancements, including bio and renewable fuels on several fronts, and no-lead avgas replacements, domestically and internationally. In addition to the development of these products, Avfuel Technology Initiatives Corporation thinks through the logistics of market introduction to help ensure any new product is sustainable, reliable, competitively priced, and fairly accessible.


Learn More

Keith Sawyer, manager of alternative fuels | [email protected] | Mobile: 925.989.0479 | Avfuel's Office: 734.663.6466

Sustainability Initiatives  |  Request Info


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