The End of One Hundred Low Lead, GAMI's G One Hundred U L, and the Long Fight to Get the Lead Out of the Only Piston Fuel Left

The era of leaded aviation fuel is ending. Under an industry-and-government initiative called EAGLE, general aviation has committed to replacing 100 low lead (100LL) - the last leaded transportation fuel in the United States - with a safe, unleaded, drop-in replacement by the end of 2030. The fuels already exist and approvals are underway; the open questions are which fuel wins, how fast it deploys, and who pays for the transition.

Why Is Leaded Avgas Being Phased Out?

The blue-tinted fuel in your Cessna, Piper, or Cirrus contains tetraethyl lead, an additive that prevents the fuel from detonating before the spark plug ignites it. In a high-compression aircraft engine, uncontrolled detonation can destroy pistons and cylinders within minutes. Lead has done that job reliably for decades.

But it is also the last leaded transportation fuel in the country. Automobiles stopped burning leaded gasoline in 1996. Piston aircraft are the only holdouts, and that distinction has finally caught up with the industry.

In the fall of 2022, the Environmental Protection Agency (EPA) issued an endangerment finding - a formal determination that lead emissions from piston aircraft contribute to air pollution that endangers public health. That finding is the legal foundation for eventually restricting or banning lead in avgas. Once it’s on the books, the regulatory machinery begins to turn.

What Is the EAGLE Initiative and the 2030 Deadline?

The FAA and industry didn’t wait to be forced. In 2021, a coalition formed under the banner EAGLE - Eliminate Aviation Gasoline Lead Emissions. It’s a joint effort between the Federal Aviation Administration (FAA) and nearly every major industry group, including the Aircraft Owners and Pilots Association (AOPA), the Experimental Aircraft Association (EAA), engine makers, airframe manufacturers, fuel producers, and airports.

Their shared goal: get a safe, unleaded, drop-in replacement fuel into the fleet by the end of 2030 - roughly four and a half years from today. If you fly anything with a piston engine and a propeller, this affects you.

Why Can’t We Just Remove the Lead?

Because of the detonation problem. About two-thirds of the piston fleet - small trainers and light singles - will run fine on lower-octane unleaded fuel. An approved option already exists: Unleaded 94 (UL94), which is essentially 100LL with the lead left out.

The challenge is the other one-third: high-compression, high-performance engines like turbocharged Bonanzas and the big Continentals and Lycomings in Cirrus singles, Cessna singles, and twins. Those engines need the full 100 octane - without lead. And here’s the catch: that one-third of the fleet burns roughly two-thirds of all avgas sold. Cracking that chemistry has taken decades.

The fuel isn’t the only thing that has to change. The entire distribution system is built around a single grade - one tank at the refinery, one truck, one tank at the airport, one pump. Introducing a new fuel forces small FBOs to decide whether to add a second tank or swap the old fuel out entirely, and to figure out who pays. This is as much a logistics story as a science story.

Which Companies Are Developing Unleaded 100-Octane Fuel?

There are three tracks running in parallel.

GAMI (General Aviation Modifications, Inc.), based in Ada, Oklahoma - the company behind GAMIjectors - spent roughly 19 years developing an unleaded 100-octane fuel called G100UL. Rather than wait for an industry-wide fleet specification, GAMI pursued approval through a Supplemental Type Certificate (STC), the same mechanism used to legally install a new radio or propeller. As of 2022, GAMI’s STC covers essentially the entire fleet of piston airplanes and engines. On paper, an owner can buy the approval for their aircraft and legally burn the fuel today.

Swift Fuels, based in Indiana, already sells UL94 and is moving its own unleaded 100-octane product, 100R, through the testing process via a more traditional route toward broad approval.

The third track is the industry-wide effort under the FAA’s testing program - the Piston Aviation Fuels Initiative (PAFI) and the qualification program that followed - aiming to approve a fuel through the full standardized specification so it’s cleared for everyone at once, with no individual paperwork.

What’s the Controversy Around G100UL?

This is genuinely contested ground. Some operators and fuel suppliers have raised concerns about material compatibility - whether the fuel interacts with certain sealants, coatings, or fuel bladders over time - and about whether it might leave deposits or affect paint if spilled. GAMI has pushed back firmly, arguing the fuel has been tested exhaustively and pointing to its approval. Testing and evaluation have continued.

This remains an area where reasonable, informed people in the industry still disagree. Anyone claiming the matter is fully settled - in either direction - is getting ahead of the facts. What is not in question: unleaded avgas is coming. The only real questions are which fuel or fuels, how fast, and who pays.

Why This Matters for Pilots

The transition already went from theoretical to real in one place. In 2022, Santa Clara County, California - which operates Reid-Hillview Airport and San Martin Airport - stopped selling 100LL entirely at those fields, offering only UL94. For based pilots flying high-compression engines, that created an immediate problem: where do you get your fuel? For them, the future arrived years ahead of the 2030 deadline.

The FAA pushed back on airports unilaterally cutting off a fuel grade, because federal grant assurances generally require an airport to provide the fuel its based aircraft need. The result was a real tug-of-war between a local government trying to reduce neighborhood lead exposure and a federal agency trying to keep the fleet flying safely. That tension is the whole national story in miniature.

If you own your airplane, now is the time to learn your engine and fuel system:

• Know your compression. Determine whether you’re in the two-thirds that can burn lower-octane fuel or the one-third that truly needs full 100 octane.
• Know your approvals. Identify which STCs exist for your specific make and model, so you already know whether you can legally and safely burn unleaded fuel when it shows up on your field.

There’s genuine good news, too. Lead is hard on engines - it fouls spark plugs and builds up on valve stems, and it’s the reason pilots lean aggressively on the ground to keep plugs clean. Removing the lead eases much of that maintenance burden. For many owners, the destination is a cleaner-running engine and less time scrubbing plugs.

And for renters and students: don’t panic. The entire point of a drop-in replacement is that it behaves like the fuel you already use - similar color, same handling, same procedures, no aircraft modification, no safety compromise. When unleaded fuel arrives at your flight school, from the cockpit it should be a non-event.

The Big Picture

For a century, avgas has been a quiet miracle of consistency. A 1946 Piper Cub and a brand-new Cirrus could fuel from the same truck. That single, stable, universal grade is a major reason general aviation has kept century-old airframes flying and the fleet so durable.

Getting the lead out means changing that fuel for the first time in generations - without grounding a single airplane, destroying a single engine, or pricing small-field flying out of existence. It’s chemistry, logistics, law, and economics all at once, on a deadline. The deadline is the end of 2030. The fuels exist, the approvals are being fought over in real time, and the smart move is to treat this as part of knowing your own airplane.

For ongoing coverage, AOPA and EAA are both tracking the EAGLE effort, and the FAA publishes updates on its fuel qualification program.

Key Takeaways

• 100LL is the last leaded transportation fuel in the U.S., and the industry has committed to a safe, unleaded, drop-in replacement by the end of 2030 under the EAGLE initiative.
• The EPA’s 2022 endangerment finding provides the legal basis for eventually restricting leaded avgas.
• About two-thirds of the fleet can already use UL94, but the high-compression one-third - which burns two-thirds of all avgas - needs unleaded 100 octane, the hard problem now being solved.
• GAMI’s G100UL (approved by STC covering essentially the whole fleet as of 2022) and Swift Fuels’ 100R are the leading candidates, alongside the FAA’s industry-wide qualification track; G100UL’s material-compatibility questions remain contested.
• Owners should know their engine’s compression and available STCs now; for most, unleaded fuel means a cleaner-running engine and fewer fouled plugs.