Air travel is responsible for about 2.5% of the world’s CO₂ emissions. Not huge, you might say. Add in the non-CO₂ warming effects — contrails, water vapour, NOx — and the number is about three times as high. So when the chatter around sustainable aviation fuel began, the industry seized it like a life preserver. Airlines set targets. Governments were giving subsidies. Panels were entirely devoted to it at conferences.
The inconvenient truth is that sustainable aviation fuel is not enough.
Not even remotely.
What SAF Actually Does Well
First of all. SAF, which can be produced from feedstocks such as used cooking oil, agricultural waste, or even municipal solid waste, can reduce lifecycle carbon emissions by up to 80% compared with conventional aviation fuel. That’s genuine. That counts. It blends with standard aviation fuel in existing engines without modification at ratios presently limited to about 50%.
As far as business travellers who wish to meet their Scope 3 goals, book and claim systems offer a real solution. Book and claim systems make it possible for companies to finance SAF use without actually having to fly on it.
However, despite all that, global SAF production in 2023 met just 0.1% of demand for aviation fuel globally. Just 0.1%.
The Scale Problem Nobody Talks About Enough
Aviation consumes roughly 300 billion litres of jet fuel annually. The math on scaling SAF is brutal. Every feedstock pathway hits a ceiling — there’s only so much used cooking oil, so much agricultural residue before you’re competing with food systems or land use.
Power-to-Liquid SAF, which uses green hydrogen and captured CO₂, could theoretically scale without these constraints. But production costs are still three to five times higher than fossil aviation fuel. Nobody’s flying on PtL at scale yet.
So what fills the gap?
Case Study 1 — United Airlines’ SAF Flight Plan
In 2021, United Airlines signed what was then the largest SAF purchase agreement in aviation history — 1.5 billion gallons from Alder Fuels over 20 years. Impressive on paper. But Alder’s technology was still pre-commercial. Production timelines slipped. The deal illustrated something important: SAF commitments frequently outpace SAF supply.
United didn’t stop there. They also put money into electric and hydrogen aviation startup ZeroAvia and backed carbon capture company 1PointFive. Their approach was a template – don’t bet everything on one fuel. Spread bets across the whole decarbonisation stack. SAF was one part, not the whole picture.
Case Study 2 — KLM’s Approach at a Sustainable Aviation Fuel Event
In 2022, at a major sustainable aviation fuel event in Amsterdam, KLM publicly acknowledged something few airlines will say out loud: demand reduction matters. Their “Fly Responsibly” initiative — controversial because an airline admitting you should fly less is genuinely weird — pushed for government intervention on short-haul routes, recommending train alternatives where feasible.
KLM was simultaneously investing in SAF and arguing for structural demand management. That combination is rare. It pointed toward a reality the industry quietly understands: you cannot fuel-switch your way out of this problem if demand keeps growing at pre-COVID rates. SAF helps. But if passenger numbers double by 2050, even 100% SAF adoption barely keeps pace.
The Full Picture: What Else Is Needed
Fleet efficiency comes first. Newer aircraft like the A321neo or Boeing 787 burn 20–25% less fuel than the planes they replace. That’s not nothing. Accelerating fleet retirement cycles and incentivising newer technology matters enormously.
Hydrogen propulsion is real but narrow. ZeroAvia and Airbus both have credible hydrogen programmes, but hydrogen’s energy density makes it impractical for long-haul. Think regional routes, maybe medium-haul by the 2040s. Not transatlantic.
Demand management is the conversation nobody wants to have commercially. Frequent flyer levies, short-haul aviation taxes, high-speed rail investment — these reduce absolute demand. Several EU governments are already moving in this direction, quietly.
Carbon removals will almost certainly be needed to offset residual emissions that neither SAF nor efficiency gains eliminate. Direct air capture is expensive and energy-intensive. But the IPCC is fairly clear: aviation is one of the hardest-to-abate sectors, and some form of removal is in the math.
Frequently Asked Questions
Q1. Can sustainable aviation fuel completely replace conventional aviation fuel?
Not yet, and not any time soon. With today’s ASTM certification, you can only mix up to 50%. PtL pathways may eventually result in 100% SAF flights, but commercial scale is likely a minimum of a decade away.
Q2. Is SAF actually carbon-neutral?
It’s lower carbon; it’s not zero carbon. Lifecycle emissions are highly dependent on feedstock and production method. HEFA SAF derived from used cooking oil has about 80% lower carbon intensity than fossil aviation fuel — pretty good, but not zero.
Q3. What happened at recent sustainable aviation fuel events regarding industry commitments?
The other big theme we saw at all the big SAF events in 2023 and 2024 was the gap between airline purchase commitments and actual production capacity. Industry groups have repeatedly called for government blending mandates to reduce investment risk.
Q4. Why don’t airlines just switch to hydrogen?
Energy density. Hydrogen fuel cells have lower energy densities than jet fuel, hence requiring bigger storage tanks which cannot fit in current airplane designs. Small-scale hydrogen aircrafts are possible to design; however, designing hydrogen airliners is still a matter of physics.
Q5. What’s the single biggest barrier to SAF scaling?
Cost. SAF costs two to five times more than conventional aviation fuel depending on the pathway. Without mandates, subsidies, or a meaningful carbon price, airlines competing on ticket price have limited ability to absorb that premium.
The Honest Conclusion
SAF is necessary. It is not sufficient. Aviation’s path to net zero runs through a combination of fuel switching, fleet modernisation, demand management, emerging propulsion technologies, and carbon removal — probably all of them, in parallel, over thirty years. Any airline or government that talks about SAF as the solution is either oversimplifying or buying time.
The industry knows this. The harder question is whether the policy frameworks and investment timelines catch up before the window closes.
