The End of Leaded Avgas, GAMI's G100UL, and the Unleaded Future Being Poured Into the Fuel Trucks at Oshkosh

General aviation is the last major transportation sector still burning leaded fuel, and the effort to end that is playing out right now at EAA AirVenture in Oshkosh. A small Oklahoma company called GAMI has already won FAA approval for an unleaded replacement fuel, G100UL, that works across essentially the entire piston fleet - and the industry has set a target of removing lead from avgas by 2030. The remaining obstacles are no longer chemical. They’re logistics, economics, and pilot trust.

Why Is There Still Lead in Aviation Fuel?

Cars stopped burning leaded gasoline decades ago. So did marine engines and off-road equipment. But a huge portion of the general aviation piston fleet still runs on 100 low lead, known as 100LL, and that fuel contains tetraethyl lead - a neurotoxin that has been recognized as dangerous for roughly a century.

The reason comes down to one word: knock.

When a fuel-and-air mixture is compressed in a cylinder and ignited, you want a smooth, controlled burn that drives the piston down. What you don’t want is detonation - part of the mixture spontaneously exploding ahead of the flame front and slamming the piston with a pressure spike. Detonation is violent. It hammers bearings, cracks pistons, and can destroy an engine in minutes.

The measure of a fuel’s resistance to detonation is octane. Higher octane means more resistance. And air-cooled aircraft engines - especially the big, high-compression, turbocharged ones - are octane-hungry in a way modern automotive engines are not. A Lycoming or Continental making high power at high manifold pressure needs serious anti-knock protection or it will destroy itself.

In the 1920s, chemists discovered that adding a few grams of tetraethyl lead per gallon boosted octane dramatically and cheaply. From a pure engineering standpoint it was elegant. The problem is that it’s poison. Lead accumulates in soil, water, and people, and it is especially harmful to children’s developing brains - with no safe level of exposure.

Why Didn’t Aviation Just Switch to Unleaded Like Cars Did?

Cars got to change their engines. When automakers went unleaded, they redesigned everything around the new fuel and added catalytic converters. Aviation can’t do that.

There are more than 170,000 piston airplanes in service, many running engine designs that are, in their fundamentals, half a century old or older. You can’t recall the fleet, and you can’t tell the owner of a 1968 Bonanza that his airplane is now illegal.

That’s the brutal constraint: the replacement fuel has to work in the engines that already exist - every one of them, from little trainers to turbocharged twins. It’s the single biggest reason this transition took so long.

What Is the EAGLE Initiative and the 2030 Deadline?

The industry-wide target is an initiative called EAGLE - Eliminate Aviation Gasoline Lead Emissions. It’s a partnership between the FAA and essentially the entire general aviation industry, with the stated goal of removing lead from avgas by 2030, safely, without stranding a single airplane.

The FAA and the EPA have both studied lead around airports, and children living near busy general aviation fields show measurably higher blood lead levels. That research is the reason the entire effort exists.

What Is G100UL and How Did GAMI Get It Approved?

The name you’ll hear most is General Aviation Modifications, or GAMI, a small company out of Ada, Oklahoma. Its engineer, George Braly, and his team spent well over a decade - and a staggering amount of their own money - developing an unleaded fuel they call G100UL.

The clever part was the regulatory path. Rather than pushing a new fleet-wide fuel specification through the FAA - a process that had stalled for years - GAMI used a mechanism pilots already understand: the Supplemental Type Certificate (STC).

An STC normally approves a modification for an aircraft - a different propeller, a new avionics stack. GAMI turned that idea sideways and obtained an STC that approves their fuel for a given airframe-and-engine combination. In 2022, the FAA approved G100UL across essentially the entire piston fleet - every spark-ignition airplane in the general aviation registry.

That was a genuine milestone: for the first time, an approved unleaded drop-in fuel existed that a high-compression engine could burn without detonating.

What Are the Downsides and Open Questions?

Materials compatibility. Changing fuel chemistry changes how the fuel interacts with everything it touches - fuel bladders, O-rings, wet-wing sealants, even airframe paint. There have been reports and heated debate about G100UL staining paint and about its long-term interaction with certain seals. GAMI says the concerns are overstated and that the fuel meets its standards; some operators and airframers want more long-term fleet data first. Both positions are reasonable, because this is the kind of issue that only fully reveals itself across thousands of airplanes and thousands of hours.

It isn’t the only fuel in the race - and that’s a good thing. Swift Fuels, based in Indiana, has taken a two-step approach. It already sells an unleaded fuel called UL94, which works well for lower-compression engines like trainers and light singles that don’t need full 100 octane, and it’s developing a high-octane unleaded called 100R. Meanwhile, major refiners are working on their own 100-octane unleaded blends through the formal industry specification process. The future is likely a family of fuels rather than a single one.

Distribution and economics. This is the unglamorous factor that decides everything. It doesn’t matter how good a fuel is in the lab if you can’t buy it at the self-serve pump. Avgas moves through a vast, aging infrastructure of pipelines, trucks, and airport tanks all built around 100LL. Every tank has to be flushed and qualified, every FBO has to decide to carry the fuel, and someone has to pay the higher per-gallon cost - at least at first. That creates a chicken-and-egg problem: refiners don’t want to produce it at scale until airports carry it, and airports don’t want to carry it until pilots ask for it.

Why Oshkosh Matters for the Unleaded Transition

AirVenture at Wittman Field, drawing roughly a quarter million people this week (July 2026), is where this transition becomes real in front of the people who actually fly. Walk the grounds and you’ll find the fuel companies with displays, engine manufacturers Lycoming and Continental explaining what their engines are approved to burn, and groups like EAA hosting forums where engineers take hard questions from skeptical owners.

That’s the real value of the event. A new fuel stops being a press release and has to survive contact with a hangar full of pilots who will say so if they think they’re being sold snake oil. New avionics prove themselves here, electric demonstrators fly here, and a new fuel earns its trust here - one honest conversation at a time.

The Real Story: Unwinding a Century-Old Design Constraint

This isn’t fundamentally a story about pollution regulations. It’s a story about a design constraint aviation has carried for a hundred years. The industry built engines around a poison because it was the cheapest way to buy octane, the world changed around it, and now the challenge is to unwind that decision without grounding the fleet it helped create.

Is 2030 realistic? It’s ambitious. The approvals are largely in hand or getting there, and the molecule exists. What stands between aviation and an unleaded future now isn’t chemistry - it’s logistics, economics, and trust: getting the fuel into thousands of airport tanks and convincing a cautious pilot population that it’s safe for the airplane they love. That’s a harder problem than the chemistry ever was.

The next time you sump your tanks and the sample cup comes back blue, look at it a little differently. That blue dye means 100LL - and engineers are working to make it a museum piece. The airplane won’t change. The number on the pump will.

Key Takeaways

• General aviation is the last major sector still using leaded fuel (100LL), which contains the neurotoxin tetraethyl lead added to prevent engine-destroying detonation.
• The EAGLE initiative, an FAA–industry partnership, aims to eliminate leaded avgas by 2030 without grounding any aircraft.
• GAMI’s G100UL won FAA approval in 2022 via the STC pathway, covering essentially the entire piston fleet; Swift Fuels’ UL94 and forthcoming 100R offer additional options.
• Open concerns include materials compatibility (paint staining, seal longevity) and the need for more long-term fleet data.
• The biggest remaining barriers are logistics, economics, and pilot trust - not chemistry - centered on fuel distribution and infrastructure.