Introduction

The first commercial transatlantic flight powered by sustainable aviation fuel, or SAF, took off in November. Going forward, what is the alternative fuel’s potential—and could it make flying more eco-friendly?

The airline industry is betting big on sustainable aviation fuel, or SAF—a fuel alternative made from renewable biomass and waste products. Dozens of airlines around the globe are experimenting with it; in November, headlines buzzed following the first fully SAF-powered transatlantic flight on a commercial airline (British carrier Virgin Atlantic). But while the emissions-heavy airline sector is heralding SAF as a silver bullet to its decarbonization goals, experts say environmental pitfalls and other obstacles abound.

What is sustainable aviation fuel, and what’s spurring its popularity?

SAF is a liquid, energy-dense fuel sourced from nonpetroleum sources, known as feedstocks, including renewable plant- and waste-based products such as used cooking oil, municipal waste, and algae. Estimated to slash the carbon footprint of conventional kerosene-based jet fuel by as much as 80 percent, SAF is also attractive for the “drop-in” compatibility it offers with existing airplane technology (meaning that it’s capable of being used with existing aircraft engines and other supply infrastructure and is compatible to be safely mixed with conventional jet fuel).

Currently, SAF is positioned as the sector’s leading means of meeting pressing U.N.-set climate targets and emerging government-imposed mandates that require airlines to partially employ SAF to operate within their borders (now instated in places like the European Union, United Kingdom, and Singapore). The International Air Transport Association (IATA), a global trade association representing some 300 airlines, has committed to meeting a net-zero emissions target by 2050—and SAF is tied to a substantial 65 percent of its calculations for reaching that goal.

What are some of the challenges and barriers to entry for SAF?

Currently, 0.2 percent of aviation fuel consumed worldwide each year is SAF. “SAF use is a drop in the bucket,” says fuel expert Nikita Pavlenko of the nonprofit International Council on Clean Transportation (ICCT).

Why is that? Well, not only is SAF up to five times more expensive than standard jet fuel, but also, it’s scarce: While roughly 158 million gallons were produced in 2023, IATA says that 119 billion gallons of SAF is needed annually to reach net-zero emissions by 2050.

Costs and funding are a big part of the scalability issue. The ICCT website reports that supply is not currently where it needs to be because the funds that “airlines are throwing at SAF today are insufficient to increase supply and build true markets.” Organizations like the ICCT suggest that airlines are unlikely to voluntarily pay a premium on fuel costs since it would increase their operating costs, push airfares up, and potentially quell demand by pricing customers out of flying. Instead, these groups suggest that supply needs to be boosted via SAF government mandates as well as economic incentive programs like government subsidies and tax credits (e.g., the new credits now being offered to SAF producers in the United States via the Inflation Reduction Act).

Additionally, SAF proponents say that more capital must be made accessible to encourage startup fuel producers. Some airlines are taking the investment strategy into their own hands: United Airlines, for instance, kicked off a $200 million venture capital fund to invest in SAF technology last year.

Others, like Lufthansa and SAS, are passing on some of the cost to passengers with the option of “green fares,” typically priced at a premium, that bundle SAF usage (as well as other carbon reduction attempts like offsets) into the ticket price; other airlines, including Air France, British Airways, and JetBlue, let passengers opt in for a supplementary fee to support SAF usage and development. The nation of Singapore, meanwhile, won’t make it optional: All passengers departing on flights from Singapore will be subject to a mandatory SAF fare levy starting in 2026. (The Civil Aviation Authority of Singapore shared that costs will vary according to factors such as distance and fare class but cited some sample economy-class fare hikes on a direct flight from Singapore to Bangkok, $2.20; Tokyo, $4.40; or London, $11.75.)

For now, the gap between available SAF funding and the production needed remains wide.

So are sustainable aviation fuels actually sustainable?

Some say the term sustainable aviation fuel is an oxymoron.

SAF may be a lower-carbon fuel alternative, but it’s not a no-carbon alternative. In fact, SAF emits comparable amounts of carbon dioxide to standard jet fuel when it’s burned, though it has lower life-cycle emissions overall, owed to its feedstocks (like biomass, which helps absorb similar amounts of carbon from the atmosphere as it grows). Each SAF product generates varying life-cycle CO2 emissions and comes with other environmental considerations (like deforestation and food crop competition to make way for SAF-ready crops), based on which feedstock types and production methods are employed. Finally, current ratio requirements adhered to by the IATA limit SAF to 10 to 50 percent of the permitted fuel blend for airplanes, meaning that the remainder of the blend must be powered with conventional—and more heavily carbon-emitting—jet fuel.

Perhaps most critically, SAF remains extremely limited in supply, with doubts being increasingly cast on whether the large quantity of SAF required can be scaled quickly enough to meet the industry’s deadlines and targets.

Ultimately, leading environmentalists and analysts caution that unconstrained growth for the aviation sector, using the promise of SAF as a panacea to the industry’s decarbonization challenges, means that the airlines won’t reach their climate goals. For now, one surefire way to ensure airline emissions reduction, Pavlenko says, is this: “The least polluting flight is one that doesn’t happen.”

Credit: AFAR