Is it lift-off for sustainable aviation fuel?
Posted: February 07, 2025
Shortly before noon on November 28, 2023, a Virgin Atlantic flight bound for New York City took off from London’s Heathrow Airport. It had no paying passengers or cargo, although Virgin's founder, Richard Branson, and the UK transport minister were both on board.
The plane would have looked unremarkable from the terminal, but it marked a major milestone for decarbonizing air travel. Upon touchdown, it became the first commercial long-haul flight powered by 100% sustainable aviation fuel, or SAF.[1]
While important, that milestone is perhaps somewhat deceptive. SAF and other solutions for decarbonizing air travel are still relatively immature and expensive, and it will likely take a long time and considerable investment to meaningfully reduce aviation’s carbon footprint.
But that isn’t stopping companies from scaling up production—and experimenting with new formulas to make flying greener.
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What is sustainable aviation fuel?
Emissions from aviation have quadrupled since the 1960s and now make up 2.5% of global energy-related CO2. What’s more, the sector is forecast to double its emissions by 2050—and could end up contributing up to 25% of the global total as other industries decarbonize.
Although they have become more efficient, modern passenger planes still use thousands of gallons of jet fuel per hour. Last year, they burned through roughly 100 billion gallons in total; SAF accounted for less than 0.5%.
Legislators want to ramp up that share: starting this year, alternative fuels must make up at least 2% of the fuel used at airports in the European Union, rising to 70% by 2050. For now, engines in commercial use are not certified to fly on more than 50% SAF, and the vast majority of flights blend in a much lower amount.
SAF’s big advantage is that it is chemically similar to fossil-based jet fuel and thus can be transported, stored and burned nearly identically. By contrast, electric planes and hydrogen-fueled jets—two other options for decarbonizing air travel in the long run—would require new or remodeled planes and a whole new infrastructure around them.
Nearly all SAF in use today is produced through a process called hydroprocessed esters and fatty acids, or HEFA, in which feedstocks such as plant or algae oils, animal fats or waste greases such as cooking oils are deoxygenated and then hydroprocessed to produce a pure component for blending directly into conventional jet fuel.
There are several other approved pathways for making SAF, for example using alcohol or biomass as feedstocks. Virgin’s demo flight, which was specially approved, burned a blend made from used cooking oil and waste animal fat mixed with a small amount of synthetic aromatic kerosene derived from corn.
The problem is that SAF currently costs two to 10 times more than fossil jet fuel to produce, depending on the technology and pathway, according to the US Department of Energy. And production has not grown as quickly as expected: last year, it reached 1 million tonnes, or roughly 0.3% of global jet fuel production, according to the International Air Transport Association.
“The technologies are already available and certified for use in aircraft," says Julie Kitcher, chief sustainability officer at plane maker Airbus. “The challenge with sustainable fuels is really about getting it produced at scale, across the globe, because this is a global industry, at an affordable price.”
Grease, corn and CO2: the future of sustainable aviation fuel
Companies are trying to get there, and some have gotten big funding boosts in recent months.
In October, the US government extended nearly $3 billion in loan guarantees to two companies working to turn crops and waste products into jet fuel. Montana Renewables, a subsidiary of industrial manufacturer Calumet, wants to expand its existing renewable fuels facility in Montana to make fuels for planes and trucks from vegetable oils and leftover animal fats and greases. And Colorado-based Gevo wants to build a new refinery to turn corn into ethanol-based jet fuel in South Dakota.
LanzaJet, another US-based firm, last year opened the first commercial-scale facility to make jet fuel from ethanol in Georgia. It will supply British Airways, among others, and has an annual capacity of 9 million gallons.
To reduce SAF’s carbon footprint even further, researchers are also looking into using agricultural waste, such as the stalks, cobs, leaves and husks left over from crop harvesting, or branches and other woody residues produced during logging. Chemists at UK company Firefly Green Fuels have even turned human waste into kerosene.
Meanwhile, a growing crop of companies is turning to entirely synthetic fuels instead.[2]
Startups Twelve and Air Company are among several working to make SAF from carbon dioxide and hydrogen. They use electricity to split CO2 and water into their constituents and then recombine the resulting hydrogen and carbon monoxide into a so-called synthesis gas—a process both companies liken to industrial photosynthesis.
At the moment, companies typically use CO2 captured from industrial facilities, although they could switch to carbon captured directly from the air in the future.
Either way, their technology is garnering increased attention: Twelve raised $645 million last year and is building its first commercial-scale facility in Washington. Another company with a similar approach, Infinium, is also building a production site in Texas and has already signed deals with American Airlines to buy its fuel from next year.
Just don’t expect to hop across the Atlantic on a SAF-powered flight anytime soon.
"It's going to take a while before we can get enough fuel where everybody's going to be able to fly,” Virgin’s Branson said before his demo flight took off. “But you've got to start somewhere.”
