Sustainable Flight Takes Off: Inside the Big SAF Bet Backed by Carbon Tech

A New Era of Jet Fuel

Sustainable aviation fuel (SAF) is no longer just a talking point—it's showing real signs of growth in the U.S. After years of hype, the numbers are finally catching up. From December 2024 to February 2025, U.S. SAF output under the “Other Biofuels” category nearly doubled, rising from 22,000 to 44,000 barrels per day. That’s a huge leap, especially considering SAF made up only a sliver of the biofuel market in prior years.

What’s changed? Several new production facilities have gone live, including New Rise Renewables in Nevada and Par Pacific in Hawaii. They joined industry veterans like World Energy in California and Montana Renewables to boost overall capacity. Meanwhile, Phillips 66 and Diamond Green Diesel wrapped major SAF expansion projects in 2024, adding tens of thousands of barrels per day.

>> RELATED: U.S. Sustainable Aviation Fuel Production Takes Off as New Capacity Comes Online

United’s Big Bet on Clean Skies

Among all U.S. carriers, United Airlines stands out for taking bold steps toward net-zero emissions. Through its \$200 million Sustainable Flight Fund, United has backed three of the most promising clean-tech companies in the sector: Heirloom, Twelve, and JetZero.

These aren’t side projects. They reflect a full-spectrum strategy. Heirloom captures CO2 from the air using crushed limestone. Twelve transforms that CO2 and water into jet fuel through industrial photosynthesis. JetZero is developing a new aircraft design—the blended-wing body—that could cut fuel consumption by up to 50% per passenger mile.

This is all part of United’s push to not just offset emissions, but to remove carbon and eventually replace fossil-based jet fuel altogether.

Limestone, Hydrogen, and Carbon: A Tech Story

Heirloom’s process is a brilliant twist on a natural phenomenon. Limestone already captures CO2 in nature — Heirloom just accelerates the process. The rock is heated in a renewable-powered kiln to release its carbon dioxide. That CO2 is then either stored underground or used to create fuel. The remaining calcium oxide is mixed with water and exposed to air to start the carbon capture cycle again.

“You need CO2, you need hydrogen, you need renewable power,” said Andrew Chang, Managing Director at United Airlines Ventures. “The idea is if you can commercialize and reduce unit costs for each of those, you have ubiquity of feedstock.”

A rendition of a JetZero blended-wing aircraft with United Airlines livery. The aircraft have the potential to reduce fuel burn by up to 50% per passenger mile compared with traditional planes, United said.

Twelve’s approach is equally groundbreaking. It uses an electrolyzer to split carbon dioxide and water into carbon monoxide and hydrogen—then recombines them into synthesis gas, the base for jet fuel. The company’s new plant in Moses Lake, Washington, is expected to produce 50,000 gallons of SAF annually with up to 90% lower lifecycle emissions compared to conventional jet fuel.

>> In Other News: Ecolectro and Re:Build Manufacturing Partner to Scale Low-Cost Renewable Hydrogen in the U.S.

Why SAF is Still So Pricey

Despite these wins, SAF still costs three to four times more than regular jet fuel. In 2024, United sourced 14 million gallons of SAF — only about 0.3% of its total fuel usage. Scaling up remains a major challenge.

What’s holding it back? Production costs, hydrogen sourcing, and infrastructure gaps. Capturing CO2 is just one step—turning it into usable fuel means adding hydrogen and energy, both of which are expensive. Still, industry optimism is strong, and United is absorbing early costs in hopes of long-term payoff.

Policy Levers and Political Reality

Government incentives are helping, but their future is uncertain. The Inflation Reduction Act’s 45Z Clean Fuel Production Tax Credit offers 35 cents per gallon of SAF produced, giving startups much-needed breathing room. Lauren Riley, United’s Chief Sustainability Officer, helped shape those provisions—and she’s not backing down despite political shifts.

“What’s really interesting in the U.S. is that the states benefiting from new SAF production are largely in red states,” said Riley. “This is good for the economy. This is creating jobs in a transitioning industry.”

The SAF Coalition, formed last year, now includes over 60 members: oil companies, labor unions, tech startups, and ag groups—all lobbying for continued support. Many of the new production jobs are landing in conservative states, shifting the politics of clean fuel investment.

What It Means for the Industry

All signs point to SAF becoming a permanent player in the aviation sector. The EIA forecasts that “Other Biofuels” output—driven largely by SAF—will more than double from 2024 to 2025 and grow another 20% by 2026. Even so, SAF will still make up just 2% of total jet fuel consumption in the U.S. next year.

Still, the foundation is set. United’s investments signal confidence in SAF’s future—not just as an emissions fix, but as an economic engine.

United Airlines’ Chief Sustainability Officer Lauren Riley

“Decarbonizing aviation is fundamentally an energy challenge,” said Andrew Chang. United’s multi-pronged strategy—fuel innovation, carbon removal, and aircraft design—is a roadmap others may soon follow.

The road ahead isn’t short or cheap, but the destination? It just might be worth the flight.