Sustainable Aviation Fuel and the five production pathways racing to replace Jet-A before the mandates hit

Five different chemical pathways are racing to produce sustainable aviation fuel (SAF) as a drop-in replacement for Jet-A, and each comes with a different feedstock, cost curve, and timeline to scale. With the EU’s ReFuelEU mandate now requiring 2% SAF at all EU airports as of January 2026—climbing to 70% by 2050—the question is no longer whether SAF will arrive, but which production method will dominate.

Why SAF Mandates Are Accelerating Now

The regulatory pressure is no longer aspirational. The European Union’s ReFuelEU Aviation regulation sets legally binding requirements with financial penalties:

2% SAF blend required at EU airports (January 2026)
6% by 2030
20% by 2035
70% by 2050

ICAO has set a net-zero carbon target for international aviation by 2050. While ICAO’s framework is voluntary, regional mandates in the UK, Singapore, and Japan are following Europe’s lead with binding requirements of their own.

Pathway 1: HEFA — The One That Works Today

Hydroprocessed Esters and Fatty Acids (HEFA) is the only pathway operating at meaningful scale right now. The process takes used cooking oil, animal fats, or plant oils, hydroprocesses them to strip out oxygen, and cracks the molecules into kerosene-range hydrocarbons chemically near-identical to conventional Jet-A.

Neste (Finland) is the world’s largest producer. World Energy operates the only dedicated SAF refinery in the United States, located in Paramount, California. HEFA fuel is already approved for blending up to 50% with conventional jet fuel and is flying commercially today—United, Delta, and dozens of other carriers have burned millions of gallons.

The limitation is fundamental: feedstock scarcity. Global used cooking oil supply is finite. HEFA handles the 2% mandate comfortably, strains at 6%, and cannot reach 70%.

Pathway 2: Fischer-Tropsch Synthesis — Proven Chemistry, New Inputs

Fischer-Tropsch (FT) is a gas-to-liquids process. A carbon source is gasified into synthesis gas (carbon monoxide and hydrogen), then catalytically converted into liquid hydrocarbons. The carbon source can be biomass, municipal solid waste, or captured CO2 combined with green hydrogen.

Sasol in South Africa has operated Fischer-Tropsch chemistry since the 1950s. The technology is mature—what’s new is applying it to aviation kerosene using sustainable carbon inputs.

FT-SAF produces extremely clean fuel: near-zero sulfur and very low aromatics. Ironically, low aromatic content is a slight complication because jet engine fuel system seals were designed to work with some aromatics—one reason the 50% blend limit exists.

Pathway 3: Alcohol-to-Jet — Leveraging Ethanol Infrastructure

Alcohol-to-jet (ATJ) starts with ethanol or isobutanol, dehydrates it, oligomerizes the resulting olefins, then hydrogenates them into jet-range hydrocarbons. The advantage: the US ethanol industry already produces about 16 billion gallons per year. If even a fraction pivots to aviation kerosene, the volume problem becomes more manageable.

Gevo is building “Net-Zero One” in Lake Preston, South Dakota with 65 million gallons per year capacity. LanzaJet, spun out of Pacific Northwest National Laboratory, brought a demonstration plant online in Soperton, Georgia in 2024. For context, 65 million gallons sounds significant until you remember global aviation burns roughly 100 billion gallons of jet fuel annually.

Pathway 4: Power-to-Liquid — The Long-Term Answer With Near-Term Pain

Power-to-liquid (also called e-fuel or synthetic fuel) requires no biological feedstock. The process captures CO2 from the atmosphere or industrial sources, electrolyzes water with renewable electricity to produce green hydrogen, then combines CO2 and hydrogen through reverse water-gas shift and Fischer-Tropsch synthesis.

The theoretical appeal is enormous: the carbon emitted during combustion is exactly the carbon captured to produce the fuel. Net zero by chemistry. No land use change, no feedstock competition with food, no supply chain limits beyond renewable electricity availability.

The practical challenge is equally enormous: energy efficiency losses compound at every step. Electrolysis runs at roughly 70% efficiency, with further losses in synthesis. A gallon of power-to-liquid SAF consumes 5–6 times more electrical energy than the fuel contains. Current cost: 6–10 times conventional Jet-A.

Porsche’s Haru Oni pilot plant in Chile is testing the concept. Full-scale economics don’t work yet, but if solar/wind costs and electrolyzer manufacturing costs continue declining, power-to-liquid could become dominant—just not by 2030.

Pathway 5: Catalytic Hydrothermolysis — The Newer Contender

Catalytic hydrothermolysis (CH, also called ReadiJet) uses fats and oils similar to HEFA, but employs supercritical water rather than hydroprocessing to crack and reform molecules. The result is a fuel with a broader range of hydrocarbon types, including cycloparaffins and aromatics, more closely mimicking conventional jet fuel’s full composition.

Applied Research Associates developed this pathway. It’s ASTM-approved for blending up to 50%, but deployment remains limited.

What Pilots Need to Know

SAF is a drop-in fuel. It uses the same fuel trucks, hydrant systems, wing tanks, and fuel controls. No aircraft or engine modifications required. When blended to specification, the airplane cannot distinguish it from conventional Jet-A.

The 50% blend ceiling is being challenged. Boeing flew a 737 MAX on 100% SAF in 2024, but certification for unblended SAF across all engine types is still in progress. ASTM committee D02 is actively reviewing data to expand approvals.

This applies to turbine aircraft only. SAF replaces Jet-A and Jet-A1. The equivalent effort for piston aviation is unleaded avgas—a completely different chemistry problem.

Current Cost and Incentive Landscape

SAF currently costs 2–4 times conventional Jet-A through the HEFA pathway. Government incentives partially offset the premium:

US Inflation Reduction Act: $1.35–$1.75 per gallon tax credit depending on lifecycle carbon reduction
EU Emissions Trading System: carbon pricing that raises conventional fuel costs
Airlines absorb some premium; passengers see the rest in fuel surcharges

Production Capacity Is Growing—But the Gap Remains

Global SAF production capacity under construction has roughly doubled in the last 18 months. Projected trajectory:

~600 million liters produced in 2024
Projected capacity of 30+ billion liters by 2030

That’s massive growth, but 30 billion liters is still less than 10% of global jet fuel demand.

The Most Likely Future: A Blend of Blends

No single pathway will dominate globally. Regional feedstock and energy availability will determine the mix:

Brazil: sugarcane ethanol for alcohol-to-jet
Middle East/North Africa: solar-powered power-to-liquid
Europe: municipal waste Fischer-Tropsch plus imported e-fuels
United States: all pathways simultaneously, leveraging diverse feedstocks

Aviation remains the hardest transportation sector to decarbonize. Batteries lack energy density. Hydrogen lacks infrastructure. Liquid hydrocarbon fuels are too energy-dense, too practical, and too embedded in aviation’s ecosystem—from airport fuel farms to wing tank designs to engine combustors—to disappear. The relevant question isn’t whether aircraft will burn liquid fuel in 2050. They will. The question is whether the carbon in that fuel came from ancient petroleum or from recycled atmospheric carbon.

Key Takeaways

Five distinct SAF pathways (HEFA, Fischer-Tropsch, alcohol-to-jet, power-to-liquid, catalytic hydrothermolysis) are competing, each with different strengths and limitations
EU mandates are legally binding: 2% now, scaling to 70% by 2050, with financial penalties for non-compliance
HEFA works today but cannot scale beyond single-digit percentages of demand; power-to-liquid could be the long-term solution but needs another decade of cost reduction
SAF is fully drop-in for turbine aircraft—no modifications needed at any point in the fuel delivery or engine system
Global production capacity is growing rapidly but still covers less than 10% of demand by 2030 projections