The Unleaded Avgas Transition: What It Means for Piston Aircraft Costs, Values and Financing

Most piston airplanes burn 100LL, which is leaded avgas, not jet fuel. So the fuel change that matters to piston owners is the move to unleaded avgas, not sustainable aviation fuel (SAF). This guide covers where that transition stands as of September 2026, and what it could mean for operating costs, resale values and loans.

SAF or unleaded avgas: which applies to your airplane?

Sustainable aviation fuel is made from non-petroleum feedstocks and blended into jet fuel, so the result is used as Jet-A in turbine engines. It is a turboprop and jet topic. A spark-ignition piston engine cannot burn it. For piston owners, the only overlap is the small fleet of Jet-A-burning diesel pistons.

The rest of this guide concerns spark-ignition engines and the move away from leaded avgas.

Where the unleaded avgas transition stands (September 2026)

STC vs. fleet authorization: what an owner actually needs

Two approval paths matter for a 100-octane unleaded fuel:

• STC (available now). An owner who wants to burn G100UL or 100R today needs the aircraft covered by that fuel’s STC. The STC holder’s instructions spell out the paperwork, such as placards, a flight manual supplement and a logbook entry, and there may be a fee. The STC documents belong in the aircraft records.
• Fleet authorization (expected 2027 for 100R; targeted 2027 for UL100E). This is a broad FAA approval that would let the eligible fleet use a fuel without each owner obtaining an STC.

For low-compression engines, many of them common in trainer-class airplanes, 94-octane unleaded is a separate path. Engine makers publish which models are approved for lower-octane unleaded fuel, and the airframe may need its own approval. Check your specific engine model and airframe rather than the family name.

What the transition could mean for operating costs

There is no reliable national price series for unleaded avgas yet, and posted prices at the few airports that sell it vary. We don’t publish a projected premium or discount. What you can budget is sensitivity: how much a price gap would change your fuel bill.

For most owners, even a $1.00 gap is smaller than the variation in insurance or hangar costs between airports. It matters more for high-hour and high-burn operators. Other cost effects to watch, without budgeting on them yet:

• Maintenance. Lead is associated with spark plug fouling and deposits, so removing it may reduce those problems. Fleet-wide maintenance savings are not established, though. Follow your engine maker’s service instructions on oil and plugs for the fuel you use.
• Supply at your home field. During the transition, some fields may sell only one grade. If you are not eligible for what they sell, a fuel stop elsewhere costs time and reserves.
• STC fees and paperwork. These are small one-time costs, but plan for them if your field switches.

For the full cost-per-hour method, see aircraft operating costs explained. For fuel-saving tactics that work with any fuel, see how to reduce aircraft ownership costs. You can also run numbers with the fuel cost calculator.

What it could mean for aircraft values

As of September 2026 we are not aware of published data showing that used piston aircraft trade at a discount or premium because of fuel eligibility. The broader used market is tight: Sandhills reports used piston-single inventory down about 17% year over year as of mid-2026, with asking prices roughly flat. Over a long holding period, though, the question buyers ask could shift:

• Lower-compression engines already have a 94-octane unleaded path where the engine and airframe are approved.
• High-compression and turbocharged engines, common in high-performance singles and twins, depend on a 100-octane unleaded fuel. G100UL and 100R STCs cover much of that fleet today, and fleet authorizations are expected from 2027.
• Documentation may become a small marketing point. A buyer can more easily confirm an airplane with its fuel STC paperwork in the logs.

For broader value drivers, see evaluating used aircraft value and future piston aircraft innovations and value.

What lenders consider (hedged)

Lender underwriting for piston aircraft still centers on the borrower’s credit and liquidity, the aircraft’s value, condition and logbooks, and the down payment. As of September 2026, we have not seen lenders in the market publish fuel-eligibility requirements or adjust rates for them. Two points are still worth raising with a lender:

• Loan term vs. transition timeline. A 20-year single-engine loan (available on loans of $75,000 or more, per AOPA) or a 10–15-year twin loan will outlast the 2030 goal. If fuel eligibility ever affects marketability, it would show up in appraisals first.
• Records. Keep fuel STC documents with the aircraft records. Lenders and appraisers review logbooks, and complete records support value. See maintenance records and loan approval.

This is general information, not a lender policy. Ask the lender how it views the transition for your specific airplane. For current loan pricing (generally about 7% to 10% as of September 2026), see aircraft loan rates.

Owner and buyer checklist

• Identify your exact engine model and its approved fuel grades, including any lower-octane unleaded approval.
• Check whether your airframe and engine are covered by the G100UL or 100R STC, and what the STC paperwork requires.
• Find out what your home field sells now and whether it plans to add or switch to an unleaded grade.
• Diesel owners: confirm which jet fuel specifications, including SAF blends, the engine maker approves.
• Buyers: ask for any fuel STC documents and file them with the logbooks.
• Budget with a fuel price sensitivity line rather than a guessed unleaded price.
• Revisit the plan when fleet authorizations are granted (expected from 2027).

How this guide differs from related guides

This page covers the unleaded avgas transition and its cost, value and financing implications. For every operating cost category and the cost-per-hour formula, see aircraft operating costs explained. For a first-year budget by aircraft class, see aircraft ownership budget by class. For fuel and other cost-cutting tactics, see how to reduce aircraft ownership costs. Model-specific costs are on the cost-of-ownership hub.

Frequently asked questions