In the quest to shrink the outsized climate impact of air travel, airlines across the globe have vowed to consume vast quantities of greener jet fuel. But most airlines are lagging far behind their pledges, according to a Bloomberg Green analysis of corporate environmental filings for 2023. 

Although many airlines have promised to get at least 10% of their propellant from cleaner sources by the end of the decade, the use of sustainable aviation fuel, or “SAF,” grew from 0.04% of global aviation fuel in 2021 to 0.17% in 2023, according to estimates from the International Air Transport Association (IATA).

European airlines are trouncing competitors in the US and elsewhere. That’s due, in part, to a government mandate, with the European Union requiring airlines to use 2% SAF starting next year. Other governments are following with mandates of their own, including the UK, Singapore and British Columbia. By contrast, the US has embraced a voluntary approach, with the government offering lucrative incentives for SAF but not requiring airlines to purchase the cleaner fuels, which cost about three-times more than conventional jet fuel.“There’s a real meaningful stick forcing [European airlines] to use it,” says Nik Pavlenko, who leads the fuels team at the International Council on Clean Transportation, a nonprofit think tank. “In the US, there’s still a bit of cognitive dissonance between the 2050 net-zero claims and the excitement about SAF, and what airlines are actually willing to pay for if they don’t have to.”DHL Group leads the world in SAF adoption, getting more than 3% of its aviation fuel from cleaner sources last year. To achieve this, the Bonn, Germany-based cargo carrier purchased more lower-emission jet fuel than all US airlines combined. In stark contrast to its European competitor, Memphis-based FedEx Corp. didn’t purchase any SAF last year, despite a pledge to get 30% of its jet fuel from cleaner sources by 2030.

Air France-KLM, meanwhile, led all passenger airlines last year with 1.1% SAF. That’s more than six-times the percentage of the US leader, United Airlines Holdings Inc., which has heavily advertised its pursuit of cleaner jet fuels. It used 0.17% SAF.“Carrots, on their own—I don’t think they’re that effective,” says Marina Efthymiou, a professor of aviation management at Dublin City University Business School. She encourages governments to use both incentives and mandates to get the SAF market off the ground.

Officials at several US airlines told Bloomberg Green that they’re committed to ramping up their use of cleaner fuels. While the available supply has been limited, things are starting to pick up, say industry officials, who point to US government data showing the amount of SAF produced or imported into the country doubled in the first half of this year compared to all of 2023.

“That’s the kind of exponential growth we’ve been hoping for,” says John Heimlich, chief economist at Airlines for America, an industry trade group.But, because SAF remains significantly more expensive, adds Heimlich, mandates would cause the price of air travel to spike. “It would just make air travel more expensive and less plentiful for all the customers,” he says.United declined to comment on the SAF numbers, while a FedEx spokesperson said in an email that the recent uptick in the production of cleaner fuels is a great sign given the market’s “fits and starts of the past decade.”The task ahead for all airlines remains staggering. Aviation accounts for about 2.5% of humanity’s carbon dioxide emissions. But that number is expected to climb as air travel increases and other large sources of climate pollution, such as power plants and automobiles, move to cleaner alternatives. Battery-powered planes likely won’t have the range to handle long-haul flights, where most emissions occur; while hydrogen-powered planes could be decades from reality. This leaves cleaner fuels—made from lower-emitting sources like used cooking oil, animal tallow and energy crops—as the airline industry’s primary hope for shrinking its climate impact.Dozens of new SAF plants are expected to come online in the next several years. Diamond Green Diesel, a joint venture between Valero Energy Corp. and Darling Ingredients Inc., says that its plant in Texas, capable of producing up to 235 million gallons of SAF per year, will start operating by the end of this year.

But other highly anticipated sources of cleaner fuels have stumbled badly. Fulcrum BioEnergy, which raised over $1 billion to convert municipal waste into liquid fuels, laid off most of its staff and halted operations in May, as first reported by Bloomberg Green. The dire turn of events casts doubts on the future of Fulcrum’s flagship plant, located outside of Reno, Nevada, as well as its future garbage-to-fuels facilities planned for Indiana, Texas and the UK.

The choppy progress for new plants prompted IATA this summer to slash its estimate of future SAF production by almost 20% through the end of the decade. Meanwhile, Air New Zealand Ltd. pulled the plug last month on its 2030 climate target, citing, in part, the scarcity of lower-emission fuels.

The shortage of cleaner fuels makes DHL’s market-leading numbers more remarkable. When the company announced a plan to accelerate its emissions reductions in 2021, it pledged to spend €7 billion over the next decade to make it happen. Last year, this included €113 million to cover the extra cost of SAF versus conventional jet fuel.

“We are serious about what we are doing,” Yin Zou, DHL’s executive vice president of corporate development, told Bloomberg Green in an interview last year. “We scratch every inch of the surface of the earth trying to look for providers” of cleaner jet fuel, he added.

DHL isn’t flush with cash compared to its competitors. It notched profits of about $4 billion last year, on par with those from FedEx. Meanwhile, United Parcel Service Inc., which generated almost $7 billion in profit and has pledged to use 30% SAF by 2035, didn’t disclose its volume of cleaner fuel last year, only describing it as “not material.”

“Supply remains limited and has not reached economies of scale, making it cost prohibitive for wide adoption,” a UPS spokesman said in a written statement.

For Efthymiou, the professor in Dublin, it often comes down to the commitment of the people leading these companies. While several are taking action, she says, “some airlines are more reactive. Until they’re put in the spotlight, they will not do anything.”