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United Airlines Charts New Course with 100% Sustainable Aviation Fuel

Pioneering commercial air travel, United Airlines leads the industry with the first passenger flight using 100% sustainable aviation fuel.

By Sneha Tete, Integrated MA, Certified Relationship Coach

Created on Sep 27, 2025

Pioneering commercial air travel, United Airlines leads the industry with the first passenger flight using 100% sustainable aviation fuel.

United Airlines’ Bold Step in Sustainable Aviation

United Airlines has made history by operating the world’s first commercial flight carrying passengers using 100% sustainable aviation fuel (SAF) in one of its two engines. This groundbreaking event marks a significant milestone in the aviation industry’s journey towards decarbonization and highlights the growing corporate and technological commitment to cleaner air travel. As the aviation sector grapples with its carbon footprint, United’s SAF initiative signals a new chapter in making commercial flights more sustainable and eco-friendly.

The Flight That Changed Aviation

On December 1, 2021, a United Airlines Boeing 737 MAX 8 flew from Chicago O’Hare to Washington’s Reagan National Airport with 115 passengers on board. While it appeared like any other routine trip, this journey was extraordinary—it was the first time a passenger flight operated using 100% drop-in SAF in one engine. United’s CEO, Scott Kirby, and numerous partners in sustainable technology and aviation joined the historic voyage to witness a tangible step toward the airline’s net-zero emissions goal.

Key details about the flight:

Aircraft: Boeing 737 MAX 8
Fuel: 100% sustainable aviation fuel in one engine; conventional jet fuel in the other
Passengers: 115 total, including industry leaders and sustainable tech partners
Route: Chicago O’Hare (ORD) to Washington Reagan National (DCA)

This flight served as a global demonstration that airlines can operate using sustainable fuels without compromising flight performance or safety, setting the stage for broader industry adoption.

What Is Sustainable Aviation Fuel?

Sustainable aviation fuel (SAF) is a next-generation fuel made from renewable feedstocks, including used cooking oil, plant oils, algae, agricultural residues, municipal solid waste, and even captured carbon dioxide. These renewable resources contrast with traditional jet fuels, which are derived from untapped fossil sources. SAF can dramatically reduce the lifecycle greenhouse gas emissions of air travel.

Common feedstocks for SAF include:

Plant oils (e.g., canola, camelina, jatropha)
Algae
Fats and greases (including used cooking oil and animal fats)
Waste streams (including forest and agricultural waste)
Certain sugars and alcohols
Directly captured CO₂ from the atmosphere or industrial sources

Advanced SAF technologies such as Power-to-Liquid (PtL) convert CO₂ and renewable electricity directly into jet fuel, enabling a truly circular carbon cycle.

Environmental Impact of SAF

SAF offers substantial environmental advantages over conventional jet fuels. By switching from petroleum-based products to SAF, the aviation industry can cut lifecycle carbon emissions by up to 80%, depending on the feedstock and technology pathway used. United’s investment in next-generation SAF could turbocharge this trend, with some estimates projecting up to 90% emission reductions for certain PtL fuels compared to standard aviation kerosene.

Fuel Type	Feedstock	Typical CO₂ Reduction
Traditional Jet Fuel	Fossil crude oil	0%
HEFA SAF	Used cooking oil, fats	Up to 80%
PtL (Power-to-Liquid)	CO₂, renewable electricity	Up to 90%

By utilizing existing waste and closing the carbon cycle through innovative chemistry, SAF can help airlines decouple their operations from fossil fuel dependence and significantly lower their environmental impact.

How United Airlines Is Leading in SAF Investment

United Airlines has positioned itself at the forefront of SAF investment and deployment, establishing several initiatives and partnerships to scale up sustainable fuel production.

Largest industry commitment: United claims the largest SAF commitment in aviation, including a pledge to purchase millions of gallons annually.
Eco-Skies Alliance: Launched in 2021, this partnership includes over two dozen corporate partners who collectively contributed toward buying more than 5.7 million gallons of SAF in a single year, reducing emissions equivalent to 53,000 metric tons of CO₂.
Sustainable Flight Fund: In 2023, United spearheaded this fund, gathering over $200 million from partners like Air Canada, Boeing, and JPMorgan Chase, all aimed at boosting early-stage SAF companies.

Through these strategies, United is not just reducing its emissions—it is fostering an entire ecosystem to enable the widespread adoption of sustainable fuels throughout aviation.

Partnerships and Technological Innovation: The Twelve Investment

One of United’s most significant investments involves partnering with Twelve, a California-based startup utilizing novel PtL technologies to transform captured carbon dioxide into jet fuel. Twelve’s AirPlant™ One facility converts CO₂, water, and renewable electricity into hydrocarbons suitable for aviation, sidestepping the feedstock limitations and ethical debates of earlier biofuels.

Twelve’s patented technology: Uses non-biological feedstocks, overcoming critical scaling and sustainability hurdles present with agricultural sources.
Closed-loop carbon cycle: The CO₂ captured for fuel production is the same CO₂ released during flight, helping mitigate atmospheric buildup.
Long-term commitment: United’s 14-year agreement includes the delivery of 260 million gallons of SAF, marking one of the largest such deals in aviation history.
Facility location: Moses Lake, Washington, with an initial output of 50,000 gallons of SAF per year and growth potential as the market scales.

This partnership not only advances United’s own emission-reduction targets but also supports the scaling of SAF availability for the entire industry.

The Benefits and Challenges of Sustainable Aviation Fuel

Benefits of SAF:

Reduces net carbon emissions across the aviation sector.
Decreases dependence on fossil fuel extraction and refining.
Expands the range of renewable feedstocks—improving energy security.
Provides a drop-in solution that does not require new aircraft or engine modifications.
Promotes innovation and supports green jobs in emerging cleantech industries.

Challenges to Overcome:

Scale and supply: Current SAF production is a fraction of total aviation fuel needs. Scaling up remains a key challenge.
Cost: SAF typically costs 2–4 times more than conventional jet fuel, though economies of scale and new technological breakthroughs may shrink this gap in the coming years.
Feedstock limitations: Traditional bio-based SAF relies on waste oils and crops, which are finite and can compete with food production. Technologies like PtL offer a solution but require significant renewable energy investment.
Infrastructure: Transportation, blending, and regulatory standards for SAF must be harmonized globally for maximum impact.

A Look to the Future: Net-Zero Aviation by 2050

Global aviation produces approximately 2–3% of total global CO₂ emissions, with commercial airlines consuming tens of billions of gallons of jet fuel annually. United Airlines and partners across industry and government envision a transition to net-zero aviation by 2050—a goal supported by increasing commitments to SAF and parallel investments in new aircraft technologies, carbon capture, and operational efficiencies.

If projected SAF adoption aligns with industry plans, aviation’s carbon footprint could shrink by 40%–70% over the next two decades. This transition depends on continued policy support, scientific innovation, and broad investment partnerships to make SAF cost-competitive and widely accessible.

FAQs: Sustainable Aviation Fuel and United Airlines’ Leadership

Q: What makes United’s SAF flight unique?

A: United Airlines operated the world’s first commercial passenger flight using 100% SAF in one engine, proving that such fuels can be safely used at scale.

Q: How does sustainable aviation fuel reduce emissions?

A: SAF can reduce lifecycle emissions by up to 80–90% compared with conventional jet fuel, depending on feedstock and technology. The reductions come from using renewable resources and recycling carbon rather than extracting new fossil carbon.

Q: What is Power-to-Liquid (PtL) technology?

A: PtL turns captured CO₂ and renewable electricity into liquid jet fuels, enabling closed-loop, low-carbon air travel without relying on crops or waste oils.

Q: Why is scaling up SAF production challenging?

A: Limited feedstock availability, higher production costs, and a need for investment in new processing facilities and supply chains all present barriers to rapid scaling.

Q: What’s United’s long-term sustainability commitment?

A: United aims to achieve net-zero emissions by 2050, supported by investments in SAF, corporate alliances, and pioneering technology partnerships.

Driving the Sustainable Future of Flight

The historic United Airlines SAF flight is more than a symbolic gesture—it represents a fundamental shift in how airlines approach sustainability, technology, and collaboration. As policies tighten, customer demand grows, and environmental urgency mounts, SAF will be pivotal in decarbonizing the skies. With its early investments and public leadership, United Airlines is not merely adapting to change—it is actively piloting the future of green aviation.

References

Author

Sneha TeteBeauty & Lifestyle Writer

Sneha is a relationships and lifestyle writer with a strong foundation in applied linguistics and certified training in relationship coaching. She brings over five years of writing experience to thebridalbox, crafting thoughtful, research-driven content that empowers readers to build healthier relationships, boost emotional well-being, and embrace holistic living.

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