Every time an airline announces a "greener" flight, one acronym does the heavy lifting: SAF. Sustainable aviation fuel is the single biggest lever the industry has to cut its carbon footprint, and the International Air Transport Association (IATA) estimates it could deliver around 65% of the emissions reductions aviation needs to reach net-zero CO₂ by 2050. But what actually is it, how is it made, and does it really cut emissions the way the marketing suggests? Here is how SAF works, from feedstock to fuel tank.
What is sustainable aviation fuel?
SAF is a non-fossil jet fuel made from renewable or waste-based raw materials called feedstocks — things like used cooking oil, animal fats, agricultural and forestry residues, and even captured carbon dioxide combined with renewable electricity. The crucial point is that it is a "drop-in" fuel: once produced and certified, SAF is chemically almost identical to conventional kerosene. That means it can be pumped through existing airport hydrant systems and burned in today's engines with no modifications to the aircraft or its fuel system.
There is a catch, though. Under the governing ASTM International standard, certified SAF can only be blended up to a maximum of 50% with conventional Jet A/A-1 for most production pathways. So when an airline says it operated a flight "on SAF," it almost always means a blend — pure 100% SAF flights remain rare demonstration events rather than everyday operations.
How SAF is made: the main production pathways
There is no single recipe for SAF. Instead, there are several approved production pathways, each using different feedstocks and chemistry. As of 2024, IATA counted 11 certified SAF pathways. The four that matter most commercially are these.
HEFA — the workhorse
Hydroprocessed Esters and Fatty Acids (HEFA-SPK) is by far the most mature and widely used route. Oil-based feedstocks — plant oils, animal fats, used cooking oil and greases — are treated with hydrogen and catalysts. This strips out oxygen and reshapes the long fatty-acid molecules through hydrocracking and isomerisation, leaving hydrocarbon chains that behave just like fossil kerosene. HEFA is the cheapest and most accessible SAF, which is exactly why it dominates the market. Its weakness is supply: the world only produces so much waste oil and fat, so HEFA volumes are effectively capped by feedstock availability.
Fischer-Tropsch — gasifying waste
The Fischer-Tropsch (FT-SPK) process dates back to 1920s Germany. Solid biomass — agricultural and forestry waste, energy crops, even municipal solid waste — is gasified into a synthesis gas, which is then catalytically reassembled into kerosene-like hydrocarbons. FT fuels can offer very low lifecycle emissions, but the supply of suitable waste feedstock again limits how much can be made.
Alcohol-to-Jet — from ethanol to kerosene
Alcohol-to-Jet (ATJ-SPK) ferments or gasifies sugary, starchy or cellulosic feedstocks into an intermediate alcohol such as ethanol, then chemically converts that alcohol into jet fuel through dehydration, hydrogenation and oligomerisation. Its output depends heavily on regional agriculture and feedstock availability.
Power-to-Liquid — fuel from thin air
Power-to-Liquid (PtL), or e-SAF, is the most futuristic route. It uses captured CO₂, water and renewable electricity to synthesise fuel electrochemically — no organic feedstock required. Because it is not constrained by land or waste-oil supply, e-SAF is widely seen as the long-term path to genuinely scalable SAF. Producers claim e-SAF can use up to 1,000 times less water and 30 times less land than bio-based SAF. The trade-off today is cost and the enormous amount of clean electricity required.
Beyond these four, niche pathways exist, such as catalytic hydrothermolysis and an algae-oil variant (HC-HEFA) that is currently certified only up to a 10% blend.
How much carbon does SAF actually save?
This is where the nuance lives. SAF is not zero-carbon — burning it still releases CO₂ from the tailpipe. The savings come from the lifecycle: because the feedstock absorbed carbon as it grew, or came from waste that would have emitted anyway, the net emissions across the whole production-and-combustion chain are far lower than fossil fuel.
According to IATA, most SAF made today via the waste-based HEFA pathway delivers a lifecycle emissions reduction of around 80% compared with conventional jet fuel. Emerging technologies and new feedstocks have the potential to push that above 90%, and in some cases even achieve negative lifecycle emissions. E-SAF producers similarly target reductions of up to 90%. The exact figure varies considerably by pathway and feedstock — which is precisely why certification frameworks scrutinise feedstock sourcing, land-use change and supply-chain traceability so closely.
Where SAF stands today: tiny volumes, big price tags
For all the headlines, SAF is still a rounding error in global aviation. IATA's production tracker tells the story of fast growth from a minuscule base: output reached roughly 1.0 million tonnes (Mt) in 2024 (about 0.3% of jet fuel use), doubled to about 1.9 Mt in 2025 (around 0.6%), and is projected to reach about 2.4 Mt in 2026 — roughly 0.8% of global jet fuel. In other words, even after years of rapid scaling, SAF still represents less than 1% of the fuel aviation burns.
The other barrier is cost. SAF is currently several times more expensive than conventional kerosene, thanks to pricier feedstocks, immature production technology, thin infrastructure and high upfront investment needs. IATA likens the situation to the early days of wind and solar power: the path to lower prices runs through scale, supportive policy and coordinated investment across the energy system. Notably, IATA reported in 2025 that the first EU and UK SAF mandates had not accelerated production as hoped, instead creating unintended cost and supply pressures — a reminder that policy design matters as much as ambition.
The rules pushing SAF forward
SAF's growth is being driven as much by regulation as by airline goodwill. Three frameworks stand out. The ICAO CORSIA scheme sets the international sustainability and lifecycle criteria SAF must meet to count toward emissions obligations. In the EU, the ReFuelEU Aviation regulation — adopted in October 2023 as part of the "Fit for 55" package — obliges fuel suppliers to blend a rising share of SAF into the kerosene supplied at EU airports, starting at a 2% minimum in 2025 and climbing to 70% by 2050. And the industry's overarching target, agreed by IATA's member airlines at the 2021 AGM in Boston, is net-zero carbon emissions by 2050, a goal echoed by ICAO's Long-Term Aspirational Goal adopted in 2022.
A quick history of how we got here
SAF is newer than many travellers assume. The first test flight using biojet fuel was flown by Virgin Atlantic in 2008, and SAF was approved for commercial aircraft operations in 2011. Between 2011 and 2015, more than 20 airlines flew over 2,500 commercial flights on blends of up to 50% biojet from feedstocks including used cooking oil and camelina. A milestone came in November 2023, when Virgin Atlantic operated the world's first transatlantic flight by a commercial airline running on 100% SAF — proof that the fuel can power a widebody across an ocean, even if everyday operations remain blended.
Does SAF do anything besides cut CO₂?
Carbon is the headline, but it is not the whole story. Because SAF is cleaner-burning than conventional kerosene, it tends to produce lower sulphur and particulate emissions — e-SAF producers, for example, point to reductions in sulphur dioxide, nitrogen oxides and soot. That matters for two reasons. First, it improves local air quality around airports. Second, the soot particles in jet exhaust help seed the condensation trails (contrails) that themselves have a warming effect; cleaner fuel may help reduce that non-CO₂ impact, an area IATA flags as an active research priority. SAF can also strengthen energy security by diversifying fuel supply away from imported crude and building domestic production from locally available waste and renewable resources — one reason governments from Washington to Brussels treat it as industrial policy, not just climate policy.
How do airlines actually get SAF?
Most airlines cannot simply fill up with SAF at every airport, because supply is concentrated at a handful of production sites. To bridge that gap, the industry is building "book-and-claim" systems and registries — including a dedicated SAF registry launched through IATA — that let an airline pay for SAF produced and used elsewhere in the network while credibly claiming the environmental benefit. This keeps the physical fuel close to where it is made (avoiding wasteful trucking) while still channelling money to producers. Combined with procurement platforms that match airlines with suppliers, these mechanisms are designed to turn SAF from a local novelty into a genuinely global market.
The challenges still ahead
The honest summary is that SAF works technically but struggles economically. The feedstocks that produce the cheapest, most mature fuel (waste oils and fats for HEFA) are in limited supply. The pathways that could scale almost without limit (e-SAF) need vast amounts of cheap renewable electricity and remain expensive. Bridging that gap will require new feedstocks, new production capacity, supportive and well-sequenced government policy, and a great deal of patient investment. For aviation enthusiasts following the industry's decarbonisation story, SAF is the technology to watch — the same way fuel-efficient widebodies like the Boeing 787 Dreamliner once reshaped expectations of what a long-haul flight should cost the planet. You can explore models and collectibles of those aircraft in our Boeing 787 Dreamliner gifts collection.
The bottom line
Sustainable aviation fuel is not a silver bullet, but it is the most important tool aviation currently has to cut emissions without waiting for radically new aircraft. It drops straight into today's jets, cuts lifecycle CO₂ by roughly 80% in its most common form, and is backed by binding mandates and a 2050 net-zero target. The unfinished work is scale and cost — turning a sub-1% fuel into the backbone of a cleaner industry. If you love following where aviation is headed, SAF is one of the defining stories of the decade. Browse more for the avgeek in your life in our aviation enthusiast gifts and gifts for pilots collections.
Comments
Loading comments…