Unleaded-Avgas Adoption on the Front Range, by the Gallon

A FRISA White Paper — Front Range Institute for Sustainable Aviation

Mid-2026. A measured study, extrapolated from several days of flight data each year and revised as the data improve.

Abstract

About 78% of the leaded avgas burned over the Front Range comes from aircraft that can fly today on Swift UL94, a certified unleaded avgas on sale now. [1] The remaining fifth comes from high-powered engines that require 100-octane fuel, and two unleaded 100-octane fuels, GAMI G100UL and Swift 100R, now serve nearly the entire piston fleet. [4][5] The convertible share holds steady across four years of data and sits well above the national figure of about 30%, because training and light aircraft fly the most hours here. [3]

Method

FRISA reconstructed avgas burn from public ADS-B flight tracks within a 35-mile circle over the Denver–Boulder–Greeley corridor, covering Boulder, Rocky Mountain Metropolitan, Longmont, Erie, Centennial, and Greeley–Weld, across 2023 through mid-2026. [1] The archive holds several days of tracks each year, so the gallon and lead totals are extrapolations from those days; the convertible share stays steady across the sample and carries the result. [2]

For each track inside the circle, we multiplied engine horsepower by a throttle setting estimated from the track's speed and climb rate, and a standard fuel-burn rate, summed to gallons, then multiplied gallons by the lead content of 100LL, about 2 grams a gallon, to get lead. [1] We read each aircraft's octane need from its type code, following the FAA and ASTM fuel standards and the Swift approval list, and gave aircraft of unknown type the fleet-average fuel mix. [2] Horsepower and fuel-burn rates come from standard piston and turbine performance tables; turbine aircraft run on jet fuel and carry no lead, so they fall outside the leaded total. [1]

Numbers

Extrapolated across the sample, the tracked fleet burned about 216,000 gallons of leaded avgas and released roughly 435 kilograms of lead over the four years; about 337 of those kilograms came from aircraft that 94UL already serves. [1] The convertible share holds within two points each year, and the high-octane fifth accounts for roughly 48,000 of the gallons. Switching that four-fifths to 94UL would carry about the same share of the lead out of the corridor's avgas, with the 100-octane fuels reaching the rest.

Availability and adoption

94UL has sold nationwide since 2019 and reaches more than 100 airports, including Centennial and Rocky Mountain Metropolitan. [5] For the high-octane fifth, GAMI G100UL holds an FAA approval covering nearly the whole piston fleet and sells at a handful of airports today, and Swift 100R earned its production standard in 2025 and now covers about 840 engine models, widening each year. [4][5] A fleet-wide FAA authorization is expected around 2027, the FAA aims to end leaded avgas by the end of 2030, and Colorado law requires five Front-Range airports to stop selling it by January 1, 2030. [6][7]

Where 94UL already sells, eligibility runs ahead of adoption. Colorado holds 94UL at the price of 100LL through a state subsidy, and at Centennial, after two years at that parity, 94UL reached about 20% of the avgas sold, against a fleet that is roughly two-thirds compatible. [8] With price matched, habit and the continued presence of 100LL on the ramp govern the rest. Elsewhere, where 94UL is unsubsidized, it commonly sells about a dollar a gallon above 100LL, which adds its own friction. [9] Engine specifics shape the switch too: one university flight school moved a training fleet to 94UL in 2023 and returned to leaded fuel after valve-seat wear, which Lycoming and Swift then investigated. [11] Familiarity and trust weigh alongside price and supply; pilots favor a fuel they have flown behind and watched others use, so adoption rises unevenly across fields, faster where operators and flight schools commit to it. Adoption climbs as leaded fuel leaves the ramp. Santa Clara County, California, marks the upper bound: removing leaded fuel in 2022 carried unleaded to nearly all of sales, until the FAA ordered 100LL restored in 2025. [10]

Notes and sources

1. FRISA, "Aviation leaded-avgas burn and Swift-94UL convertibility over the Front Range, from multi-year ADS-B," computed 2026-06-30. In-region fuel-burn integration over archival ADS-B tracks within 35 nm of the corridor centroid, classed by type per ASTM D910 and D7547, the Swift STC list, and Lycoming SI 1070; lead per EPA-420-R-20-003. A measured, reproducible result. Frozen data: research/unleaded-transition/frontrange-adsb-fuel-history.json; method and pre-registration: /research/unleaded-transition/PRE-REGISTRATION.html
2. The archive samples several days of tracks per year and favors higher-altitude transponder-equipped traffic, so annual gallons and lead are extrapolations from the sample while the convertible share holds across it. Throttle is estimated from each track, accurate in aggregate; aircraft of unknown type receive the fleet-average fuel mix; 100LL carries up to 2.12 grams of lead per gallon under ASTM D910.
3. AOPA, "100 Unleaded Avgas" — the national split of roughly 70% of airframes and 30% of fuel volume eligible for 94-octane unleaded. https://www.aopa.org/advocacy/100-unleaded-avgas
4. General Aviation News, "GAMI fleetwide STC for G100UL," 2022 — FAA approval for nearly every spark-ignition piston engine and airframe. https://generalaviationnews.com/2022/09/03/gami-unleaded-fuel-approved-for-all-general-aviation-aircraft/
5. AOPA, "FAA expands Swift 100R unleaded approval," Mar. 20, 2026 — ASTM production spec in 2025, about 840 engine models approved; UL94 at 100+ airports with 5M+ gallons delivered. https://www.aopa.org/news-and-media/all-news/2026/march/20/faa-expands-swift-unleaded-approval
6. FAA, EAGLE — a lead-free piston fleet by the end of 2030, with a fleet-wide authorization expected around 2027. https://www.faa.gov/newsroom/faa-industry-chart-path-eliminate-lead-emissions-general-aviation-end-2030
7. Colorado HB24-1235 (2024); CDOT Aeronautics — five Front-Range airports end leaded sales by Jan. 1, 2030, with state subsidy and infrastructure funding. https://www.codot.gov/programs/aeronautics/unleaded-avgas-transition-hb1235-implementation
8. Centennial Airport, "Unleaded Avgas Program" — UL94 about 20.5% of avgas sold by May 2025 at price parity; roughly two-thirds of the fleet compatible. https://www.centennialairport.com/unleaded-avgas-program
9. Field prices via AirNav and General Aviation News fuel-price reporting — where 94UL is unsubsidized it commonly sells about a dollar a gallon above 100LL (for example $7.05 vs $5.39, and $6.25 vs $5.16). Colorado's HB24-1235 subsidy holds 94UL at 100LL parity at its program airports. https://generalaviationnews.com/2026/06/04/100ll-fuel-prices-climb/
10. General Aviation News — Santa Clara County's 2022 removal of leaded fuel carried unleaded to nearly all sales before the FAA ordered 100LL restored in 2025. https://generalaviationnews.com/2025/03/28/faa-orders-california-county-to-reverse-100ll-ban/
11. FlyingMag — the University of North Dakota returned a training fleet to leaded fuel in 2023 after valve-seat wear on UL94, prompting a Lycoming and Swift investigation. https://www.flyingmag.com/university-of-north-dakota-stops-ul94-use-following-valve-recession-concerns/