By Li Qiao
The federal spending law passed in early July 2025, often called the One Big Beautiful Bill Act, significantly reduces federal funding for efforts to create renewable or sustainable types of fuel that can power aircraft over long distances while decreasing the damage aviation does to the global climate.
Aviation contributed about 2.5% of global carbon emissions in 2023. It’s particularly hard to reduce emissions from planes because there are few alternatives for large, portable quantities of energy-dense fuel. Electric batteries with enough energy to power an international flight, for instance, would be much larger and heavier than airplane fuel tanks.
One potential solution, which I work on as an aerospace engineer, is a category of fuel called “sustainable aviation fuel.” Unlike conventional jet fuel, which is refined from petroleum, sustainable aviation fuels are produced from renewable and waste resources — such as used cooking oil, agricultural leftovers, algae, sewage and trash. But they are similar enough to conventional jet fuels that they work in existing aircraft tanks and engines without any major modifications.
Prior to Donald Trump’s second term as president, the U.S. government had set some bold targets: by 2030, producing 3 billion gallons of this type of fuel every year, and by 2050, producing enough to fuel every U.S. commercial jet flight. But there’s a long journey ahead.
Leon Neal/Getty Images
A range of source materials
The earliest efforts to create sustainable aviation fuels relied on food crops – turning corn into ethanol or soybean oil into biodiesel. The raw materials were readily available, but growing them competed with food production.
The next generation of biofuels are using nonfood sources such as algae, or agricultural waste such as manure or stalks from harvested corn. These don’t compete with food supplies. If processed efficiently, they also have the potential to emit less carbon: Algae absorb carbon dioxide during their growth, and using agricultural waste avoids its decomposition, which would release greenhouse gases.
But these biofuels are harder to produce and more expensive, in part because the technologies are new, and in part because there are not yet logistics systems in place to collect, transport and process large quantities of source material.
Some researchers are working to create biofuels with the help of genetically modified bacteria that convert specific raw materials into biofuel. In one method, algae are grown to produce sugars or oils, which are then fed to engineered bacteria that turn them into usable fuels, such as ethanol, butanol or alkanes. In another effort, photosynthetic microbes such as cyanobacteria are modified to directly convert sunlight and carbon dioxide into fuel.
All these approaches – and others being explored as well – aim to create sustainable, carbon-neutral alternatives to fossil fuels. Exciting as it sounds, most of this technology is still locked away in labs, not available in airports.
Blends are being tested
At present, the U.S. Federal Aviation Administration allows airlines to fuel their aircraft with blends of up to 50% sustainable aviation fuel, mixed with conventional jet fuel. The exact percentage depends on how the fuel was made, which relates to how chemically and physically similar it is to petroleum-based jet fuel, and therefore how well it will work in existing aircraft tanks, pipes and engines.
There are two major hurdles to wider adoption: cost and supply. Sustainable fuels are much more expensive than traditional jet fuel, with cost differences varying by process and raw material. For instance, the raw price of Jet-A, the most common petroleum-based aviation fuel, had a wholesale price averaging US$2.34 a gallon in 2024, but one type of sustainable fuel wholesaled at about $5.20 a gallon that year.
The federal budget enacted in July 2025 reduces government subsidies, effectively raising the cost of making these fuels.
In part because of cost, sustainable fuel is produced only in small quantities: In 2025, global production is expected to be about 2 million metric tons of the fuel, which is less than 1% of the worldwide demand for aviation fuel. There is international pressure to increase demand – starting in January 2025, all jet fuel supplied at airports in the European Union must include at least 2% sustainable fuel, with minimum percentages increasing over time.
Planes can use these fuels
Companies such as General Electric and Rolls-Royce have shown that the jet engines they manufacture can run perfectly on sustainable fuels.
However, sustainable aviation fuels can have slightly different density and energy content from standard jet fuel. That means the aircraft’s weight distribution and flight range could change.
And other parts of the aircraft also have to be compatible, such as those that store, pump and maintain the balance of the fuel. That includes valves, pipes and rubber seals. As a visiting professor at Boeing in the summer of 2024, I learned that it and other aircraft manufacturers are working closely with their suppliers to ensure sustainable aviation fuels can be safely and reliably integrated into every part of the aircraft.
Those finer details are why headlines you may have seen about flights that burn “100% sustainable aviation fuel” are not quite the full story. Usually, the fuel on those flights contains a small amount of conventional jet fuel or special additives. That’s because sustainable fuels lack some of the aromatic chemical compounds found in fossil-based fuels that are required to maintain proper seals throughout the aircraft’s fuel system.
Good promise, with work ahead
While many details remain, sustainable aviation fuels offer a promising way to reduce the carbon footprint of air travel without reinventing or redesigning entire airplanes. These fuels can significantly cut carbon dioxide emissions from aircraft in use today, helping reduce the severity of climate change.
The work will take research, and investment from governments, manufacturers and airlines around the world, whether or not the U.S. is involved. But one day, the fuel powering your flight could be much greener than it is now.
Li Qiao is Professor of Aeronautics and Astronautics at Purdue University.
Joe D says
OF COURSE, they cut research funds into a less fossil fuel containing (or possibly NO FOSSIL FUEL containing) aviation fuel!
Less need for fossil fuel will HURT the PROFITS of President Trump’s fossil fuel buddies.
And for those of you that talk about cutting government WASTE, by cutting expensive (as MOST new technologies are in the initial development stage) research costs into this renewable/sustainable aviation fuel….the BIG BEAUTIFUL BILL passing through the Senate, although cutting subsidies for alternative (non polluting or greenhouse gas producing) energy sources (solar/wind/geothermal)…the Big Beautiful Bill left government subsidies INTACT for fossil fuel companies …GEE…I wonder how THAT happened.
Those continued fossil fuel federal government subsidies were the starting point for the RIFT between Elon Musk and Donald Trump
Deborah Coffey says
This is fascinating! But once again, the MAGA government will only pass bills that keep the oligarchs happy by making them richer. How to achieve that? Take everything away from “We the People”…our health, our wealth, our rights, and our safety. Only invest in the oligarchs. What will the MAGAs do when they realize that even THEY cannot survive on the very planet they are destroying? That day is coming much sooner than they will acknowledge.
Pogo says
@Trump
… one word — to convey the acme of destructiveness, uselessness, and ugliness.
RobdaSlob says
Probably for the sake of brevity the author simplified what is a very complex geopolitical / engineering problem.
US government funding is only part of the story.
On the geo-political: The European Union has led in the messaging and desire. They have not been successful in getting everyone aligned with the objective and as a result people are going to say – you want it, you pay for it. And people stand to make a lot of money if solutions are mandated so shouldn’t those that stand to gain the most, pay the most? Fair questions whether I agree or not.
On the engineering side: The lift is significant. And the author didn’t recognize the steps that must be overcome. Such as:
1) The industry needs to come to an agreed standard. Jet A mentioned in this article is made to an industry standard ASTM D1655. The “SAF” flights mentioned here in the article are baby steps. When SAF is used on a certified aircraft today the fuel that is put in the tank still meets ASTM D1655. It is just blended with something other than fossil fuel. What is needed is an equivalent to ASTM D1655 for SAF.
2) He touched on the feedstock. But we live in a complex world and the industry has already experienced scenarios where when the feedstock is traced back to its source it is not as claimed by the producer. Taking food off of peoples plates to make jet fuel is not a path to success.
3) There are flights being conducted on airplanes with pure SAF but because there isn’t an agreed standard than it is just part of the journey to develop to reach that standard. That can fool people in to thinking that we are there and what is holding this up…
3) Without an agreed standard the FAA cannot certify it for use. Right now they would have to certify effectively every refiner’s process and then every aircraft that uses that refiner’s fuel. E.g. today the FAA certifies every jet to use ASTM D1655 and as long as producer of fuel can show they meet that standard they are good to go. Without a standard they would have to certify each company – Shell, Exxon, etc. – going through and agreeing to the process they are using to create the fuel. And then approve each model airplane is ok to use that manufacturer’s fuel.
4) Without an agreed standard the industry cannot produce the infrastructure to support the fuel. Today jet fuel is moved around through pipelines and trucks with required filtration, water mitigation, handling criteria, etc. Can I put Jet A in my airplane when SAF isn’t available or do I have to purge the tanks and introduce the next fuel or….?
5) Emissions – there is concern today that the emissions from jet A are overly damaging our environment. The test methodologies for measuring tailpipe emissions at altitude are just now converging. Which is great because we would all feel pretty stupid if we put all this effort into a new fuel and then it turns out to be more harmful than what we started with.
There are solutions for all of these problems but in a broad industry such as aerospace it takes long term strategic thinking to build consensus and push these through. So the challenge will span across multiple administrations. Everyone knew the current one was going to tilt away but the pendulum will continue to swing.