Sustainable Aviation Fuel, the Feedstock Math That Exposes the Scale Problem, and the Power-to-Liquid Pathway That Might Actually Work

Sustainable aviation fuel - SAF - is chemically nearly identical to conventional Jet-A. It works in existing engines, existing aircraft, and existing fuel infrastructure without modification. The case for it starts with a hard physics constraint: aviation will be burning liquid hydrocarbons for the next several decades, and the only real question is where those hydrocarbons come from.

Why Batteries and Hydrogen Don’t Solve Aviation’s Fuel Problem

Jet-A carries roughly 43 megajoules per kilogram. The best lithium battery cells available today deliver approximately 250–300 watt-hours per kilogram - which works out to about 1 MJ/kg. That’s a 40-to-1 energy density disadvantage, and that gap matters far more at 350 knots at FL310 than it does in a car.

Hydrogen is better than Jet-A on a per-kilogram basis, but its volumetric density is poor even when liquefied, and storing cryogenic liquid hydrogen in aircraft presents a fundamentally different engineering challenge. Neither path offers a near-term drop-in solution for the existing global fleet.

SAF does. That’s the premise, and it’s a sound one.

How SAF Is Made: The Approved Pathways

The certification framework comes from ASTM International, specifically standard D7566, which defines approved production pathways and blending requirements.

HEFA (hydroprocessed esters and fatty acids) is the most commercially mature pathway today. It takes bio-based fats and oils - used cooking oil, animal fats, agricultural residues - and hydroprocesses them, stripping oxygen molecules and rearranging carbon chains into a hydrocarbon nearly indistinguishable from conventional kerosene. Neste, the Finnish company, is the largest SAF producer in the world and HEFA is their primary process. World Energy operates a HEFA facility in California.

Alcohol-to-jet (ATJ) ferments sugars or cellulosic biomass into ethanol or isobutanol, then converts that alcohol into jet fuel through a series of chemical reactions. The feedstock pool is broader than HEFA - municipal solid waste and forestry residue qualify - but conversion efficiency is lower and the lifecycle carbon accounting becomes complicated once you factor in land-use shifts.

Fischer-Tropsch synthesis gasifies a feedstock to produce synthesis gas, then runs it through a catalytic reactor to produce liquid hydrocarbons. Sasol, the South African company, has done this with coal for decades. The problem is that coal-based Fischer-Tropsch produces lifecycle emissions worse than conventional Jet-A. The process only helps when the input is waste biomass and the facility runs on renewable energy.

The Feedstock Math That Exposes the Scale Problem

Here is the number that reframes every optimistic SAF headline. Global jet fuel consumption runs approximately 300 million metric tons per year. Current SAF production across all pathways and all producers is measured in hundreds of thousands of metric tons per year - a gap of roughly three orders of magnitude.

The ceiling for HEFA is even more constraining than the current production number suggests. When researchers total up every theoretically available unit of used cooking oil, tallow, and waste agricultural fat on Earth and calculate the maximum possible HEFA output, the result is somewhere between one and five percent of global jet fuel demand. Not current production - the theoretical ceiling. If every fryer and every rendering facility redirected all output to aviation, the industry still wouldn’t reach five percent of need.

That is not a technology problem. That is a finite planet problem.

IATA has committed to 65% of aviation’s net carbon reduction coming from SAF by 2050. Getting from under 1% today to 65% of need in roughly 24 years requires production to approximately double every two to three years, consistently, without interruption, for a quarter century. No manufacturing scale-up in modern history has maintained that trajectory without pause.

Power-to-Liquid: The Pathway That Sidesteps the Feedstock Ceiling

There is one production pathway that doesn’t compete for finite biological feedstocks. The industry calls it power-to-liquid, or e-fuel, or electrofuel.

The inputs are carbon dioxide captured from the atmosphere and water. Electricity splits the water into hydrogen and oxygen through electrolysis. That hydrogen is then combined with the captured CO₂ through Fischer-Tropsch or methanol synthesis. The output is synthetic kerosene - a liquid hydrocarbon fuel with the same energy density as Jet-A.

The carbon in that fuel came from the air. When it burns, it returns to the air. If the electricity powering the entire process comes from renewable sources, the net atmospheric carbon addition is approximately zero. This is, in principle, a genuinely carbon-neutral liquid fuel.

Companies actively developing this pathway include Norsk e-Fuel in Norway, building facilities designed to use offshore wind and direct air capture; Haru Oni in southern Chile, using Patagonian wind power; Infinium in the United States; and Ineratec in Germany.

The thermodynamics are inefficient by design. Producing one unit of energy as liquid hydrocarbon through the power-to-liquid process requires roughly four to six units of electrical energy input. You are storing renewable electricity in chemical form, with significant conversion losses at electrolysis, carbon capture, and synthesis. Current cost estimates place power-to-liquid SAF at three to eight times the price of conventional Jet-A, depending on local electricity costs and facility scale. Some analysts project it could approach cost parity sometime in the 2030s or 2040s with very low-cost renewable electricity at commercial scale.

The honest answer is that no one knows with precision, because no power-to-liquid facility has yet operated at anything close to the scale aviation requires.

What the Policy Environment Is Doing to Accelerate Investment

The policy landscape has shifted meaningfully and is now driving capital into SAF production in ways that didn’t exist a few years ago.

The Inflation Reduction Act in the United States created production tax credits for SAF that scale with the lifecycle carbon reduction achieved. Fuel achieving a 50% lifecycle reduction versus conventional Jet-A qualifies for a meaningful per-gallon credit; larger reductions earn larger credits. That framework changed the investment calculus for producers almost immediately.

The European Union’s ReFuelEU Aviation mandate goes further. It requires fuel suppliers at EU airports to blend a minimum SAF percentage that starts small and ramps up significantly over coming decades. The target is 70% by 2050. This is a legal requirement with financial penalties for non-compliance - not a voluntary corporate sustainability pledge. It is a regulatory forcing function with teeth.

What This Means for Pilots Right Now

Under ASTM D7566, most approved SAF pathways are certified for blending at up to 50% SAF blended with 50% conventional Jet-A. The SAF you encounter at airports today is almost certainly a blend. It is functionally identical to Jet-A in every performance characteristic that matters operationally - same flash point, same freeze point specification, same viscosity range. No aircraft modifications, no engine derating, no different handling procedures.

There is one practical planning note worth filing. SAF blends can have slightly different energy density by volume compared to conventional Jet-A because molecular composition varies by pathway and feedstock. The difference is typically within a few percent. For routine operations it falls within the noise. For a tight mountain crossing with calculated reserves, it is worth a moment’s thought - check whether your POH fuel burn numbers were derived from conventional Jet-A and whether any applicable service information addresses SAF blends.

The near-term supply reality: SAF production is concentrated at a small number of large facilities, and distribution follows production volume. Major hubs get SAF first. The FBO at your local uncontrolled field is selling conventional Jet-A today and will continue to do so for some years.

The Larger Stakes

Commercial aviation represents approximately 2–3% of global CO₂ emissions. When non-CO₂ climate effects at altitude are included - contrail formation and upper-atmosphere chemistry - the effective climate forcing is closer to 4%. That number is not going away, and the industry cannot defer addressing it indefinitely.

The structural advantage of power-to-liquid SAF over electrification is significant and often underappreciated. Electrification requires replacing the entire fleet, rebuilding infrastructure, and redesigning aircraft from first principles. Power-to-liquid SAF requires changing only the molecule source. Every existing aircraft, every existing engine, every fuel truck, every wing sump - all of it stays the same.

The inputs for power-to-liquid are effectively unlimited: sunlight, wind, water, and atmospheric CO₂. It does not compete with food agriculture. It does not depend on a specific waste stream. The engineering challenges are real - direct air capture currently costs hundreds of dollars per metric ton of carbon captured, and the synthesis facilities are capital-intensive. But the physics is not in dispute and the chemistry is proven at small scale. The open questions are economic and political: whether renewable electricity gets cheap enough fast enough, whether carbon capture scales with acceptable efficiency, and whether policy stays stable enough to justify the long-term capital commitments the technology requires.

Key Takeaways

Aviation’s energy density requirements make battery and hydrogen alternatives impractical for commercial-scale flight in the near term; liquid hydrocarbons remain the physics-constrained answer
HEFA is the most commercially mature SAF pathway today, but its theoretical ceiling is only 1–5% of global jet fuel demand due to finite biological feedstock availability
Current SAF production is roughly 1,000 times smaller than global jet fuel demand - closing that gap by 2050 requires sustained exponential growth with no historical precedent
Power-to-liquid (e-fuel) sidesteps the feedstock ceiling entirely, using renewable electricity, atmospheric CO₂, and water - but current costs run 3–8x conventional Jet-A and no facility has operated at meaningful scale
SAF blends available today are true drop-in replacements requiring no aircraft or engine modifications; pilots should note that slightly varying volumetric energy density warrants a check on tight fuel planning calculations