Every time a commercial jet takes off, it burns through thousands of gallons of fuel. A single transatlantic flight can consume enough jet fuel to fill several swimming pools. And with over 100,000 flights happening every day worldwide, aviation accounts for roughly 2-3% of global carbon dioxide emissions—a number that’s been climbing steadily as more people take to the skies.
Here’s the challenge: we can’t just switch jets to electric batteries like we’re doing with cars. The energy density required to lift hundreds of people and their luggage across continents demands something more concentrated than today’s batteries can provide. So how do we keep connecting the world through air travel without cooking the planet?
Enter sustainable aviation fuel, or SAF—a technology that’s turning cooking oil, agricultural waste, and even captured carbon dioxide into jet fuel that works in today’s aircraft. Let’s explore how we’re learning to power jets with leftovers.
The Restaurant Oil Analogy
Think of sustainable aviation fuel like taking used cooking oil from restaurants and turning it into high-performance racing fuel. Instead of drilling new oil wells, we’re taking materials that would otherwise be waste—or materials that recently absorbed carbon from the atmosphere—and converting them into a fuel that’s chemically similar enough to traditional jet fuel that planes can’t tell the difference.
It’s recycling elevated to an industrial art form, and it could help us clean up one of the most stubborn sources of carbon emissions.
Why Electric Jets Aren’t Happening Yet
Before we dive into SAF, let’s understand why we can’t just electrify airplanes the way we’re electrifying cars.
The core problem is energy density—how much energy you can pack into a given weight. Jet fuel contains about 12,000 watt-hours of energy per kilogram. The best lithium-ion batteries today? Around 250 watt-hours per kilogram. That’s nearly 50 times less energy for the same weight.
Imagine trying to drive cross-country, but your car needs a battery that weighs as much as a school bus to make the trip. That’s the challenge aviation faces. Every extra kilogram on a plane requires more energy to lift and carry, creating a vicious cycle where heavier batteries need more batteries to do the same work.
This is why hydrogen and electric planes are limited to small aircraft on short routes—the physics just don’t work for long-haul flights carrying hundreds of passengers. At least not with current or near-term battery technology.
What Makes Fuel “Sustainable”?
Traditional jet fuel comes from crude oil that’s been underground for millions of years. When we burn it, we’re releasing carbon that was locked away—carbon that adds to the atmosphere’s total.
Sustainable aviation fuel takes a different approach. The “sustainable” comes from where the carbon originates and how the fuel is produced. There are several pathways:
Biofuels from organic matter: These fuels are made from plants, agricultural waste, used cooking oil, or even algae. The key is that these sources recently absorbed carbon from the atmosphere as they grew. When you burn the fuel, you’re releasing carbon that was recently captured—creating a closed loop rather than adding new carbon to the atmosphere.
Power-to-liquid synthetic fuels: These fuels are made by capturing carbon dioxide from the air or industrial processes and combining it with hydrogen (ideally produced using renewable electricity). You’re essentially creating a liquid fuel from the atmosphere’s existing carbon and renewable energy.
Waste-to-fuel processes: These convert materials like agricultural residues, forestry waste, or municipal solid waste into jet fuel. Instead of letting organic waste decompose and release methane (a potent greenhouse gas), we convert it into useful fuel.
The Drop-In Solution
Here’s what makes SAF particularly clever: it’s designed to be a “drop-in” fuel. This means it’s chemically similar enough to conventional jet fuel that it can be mixed with traditional fuel—or even used alone in some cases—without any modifications to aircraft engines, fuel systems, or airport infrastructure.
Think of it like using premium unleaded gasoline in a car designed for regular unleaded. The engine doesn’t know the difference because, chemically, they’re compatible. The molecules might come from different sources, but they behave the same way when burned.
This drop-in compatibility is crucial. The global aviation fleet represents trillions of dollars in aircraft that will keep flying for decades. Redesigning every plane would be prohibitively expensive and time-consuming. SAF lets us start reducing emissions now, using existing infrastructure.
How SAF Is Made: The Major Pathways
Creating sustainable aviation fuel isn’t a single process—it’s a collection of different technologies, each with its own advantages and challenges.
HEFA: The Cooking Oil Route
Hydroprocessed Esters and Fatty Acids (HEFA) is currently the most common pathway for producing SAF. It’s essentially taking fats and oils—used cooking oil, animal fats, or plant oils—and converting them into jet fuel through a chemical process.
Here’s the basic idea: fats and oils are chains of carbon and hydrogen atoms, not too different from petroleum. Through hydroprocessing (adding hydrogen under heat and pressure), these chains are broken down and rearranged into molecules that match jet fuel specifications.
HEFA fuel can already be used as a 50/50 blend with conventional jet fuel and meets all safety and performance requirements. Some airlines are using it today. The limitation? We can only collect so much used cooking oil and animal fat—there’s not enough to power all of aviation.
Fischer-Tropsch: Waste into Fuel
The Fischer-Tropsch process, originally developed in the 1920s, converts carbon monoxide and hydrogen (synthesis gas, or “syngas”) into liquid hydrocarbons.
For sustainable fuel, you create syngas from biomass—wood chips, agricultural residues, municipal solid waste, or other organic materials. Through gasification (heating in a low-oxygen environment), you break down complex organic materials into simple gases, then build them back up into jet fuel molecules.
It’s like deconstructing a house into basic materials, then reassembling those materials into a different building. The process is more complex than HEFA, but it can use a wider range of feedstocks—essentially anything that was recently alive can potentially become fuel.
Alcohol-to-Jet: The Fermentation Path
This pathway is similar to making ethanol fuel, but with additional steps to create jet fuel instead of simple alcohol.
You start with sugar or starch-rich materials (corn, sugarcane, agricultural waste) and ferment them into alcohol—the same basic process used to make beer or vodka. Then, through additional chemical processing, you convert that alcohol into molecules suitable for jet engines.
The advantage here is that fermentation is a well-understood, scalable process. The challenge is making it cost-competitive with conventional fuel while ensuring you’re not competing with food production for agricultural resources.
Power-to-Liquid: Making Fuel from Air and Electricity
This is perhaps the most futuristic approach: capture carbon dioxide from the atmosphere or industrial emissions, split water into hydrogen using renewable electricity, then combine the CO₂ and hydrogen to create synthetic hydrocarbon fuel.
The chemistry is straightforward—you’re essentially running photosynthesis in a factory. The challenge is energy efficiency. It takes a lot of electricity to split water and drive the chemical reactions. For this to be truly sustainable, that electricity needs to come from renewable sources—solar, wind, or other clean energy.
Power-to-liquid fuels could theoretically be carbon-neutral or even carbon-negative if you’re permanently removing more CO₂ than you emit. But the economics remain challenging with current technology.
The Carbon Math: How Much Cleaner Is SAF?
The environmental benefit of SAF isn’t about what happens in the engine—burning any jet fuel produces the same emissions at the exhaust. The benefit comes from the full lifecycle: where the carbon came from and how the fuel was produced.
A well-produced SAF can reduce lifecycle carbon emissions by 50-80% compared to conventional jet fuel. The exact number depends on:
- The feedstock: Used cooking oil has a different carbon profile than purpose-grown crops
- Production energy: Was the factory powered by coal or renewables?
- Transportation: How far did feedstocks travel?
- Land use changes: Did producing the feedstock require clearing forests or displacing food crops?
This is why certification and standards matter. Not all “sustainable” fuels are equally sustainable. Rigorous lifecycle analysis ensures that SAF delivers real environmental benefits and doesn’t create new problems while solving old ones.
The Challenges: Why We’re Not All Flying on SAF Today
If SAF is so promising, why aren’t we using it everywhere? Several significant hurdles remain:
The Cost Problem
SAF currently costs 2-4 times more than conventional jet fuel. That’s a massive difference for airlines operating on thin profit margins.
Why so expensive? Production volumes are still relatively small, so SAF doesn’t benefit from economies of scale. The feedstocks can be expensive—used cooking oil is now a commodity with competing uses. And the production facilities require significant capital investment.
As production scales up, costs should fall. But reaching price parity with fossil jet fuel is likely years away without policy incentives or carbon pricing.
The Scale Challenge
Global aviation consumes about 100 billion gallons of jet fuel per year. Current SAF production is measured in millions of gallons—a fraction of a percent of demand.
Building the infrastructure to produce SAF at scale is a massive undertaking. We need:
- Collection systems for waste feedstocks
- New production facilities
- Supply chains to deliver SAF to airports worldwide
- Enough sustainable feedstock to matter
Even with aggressive growth, SAF might only supply 10-20% of aviation fuel by 2040. That’s meaningful progress, but not a complete solution.
The Feedstock Limits
There’s only so much used cooking oil, agricultural waste, and other waste feedstocks available. As we scale up SAF production, we’ll increasingly need to use purpose-grown energy crops or synthetic pathways.
This raises important questions: Should we dedicate agricultural land to growing fuel when we need that land for food? How do we ensure we’re not creating new environmental problems—deforestation, water scarcity, biodiversity loss—in pursuit of sustainable fuel?
These aren’t just technical questions; they’re ethical and economic ones that require careful policy and planning.
The Blending Boundaries
Current aviation standards limit SAF to a 50/50 blend with conventional fuel in most cases. This is a safety precaution—jet fuel needs to meet strict specifications for freezing point, energy density, lubricity, and dozens of other properties.
Some SAF pathways are being certified for higher blend ratios or even 100% SAF use. But each pathway requires extensive testing to ensure it won’t cause problems at 35,000 feet. This certification process is necessary but time-consuming.
Who’s Using SAF Today?
Despite the challenges, SAF is already flying:
Airlines: Major carriers like United, Delta, British Airways, and Lufthansa have committed to purchasing millions of gallons of SAF. Some run regular flights on SAF blends.
Corporate flyers: Companies are purchasing SAF to reduce the carbon footprint of business travel. Microsoft, Amazon, and others have made significant SAF commitments.
Airports: Los Angeles, Stockholm, Oslo, and other airports now have SAF available for any airline to use, blended into the regular fuel supply.
Military applications: The U.S. Air Force and other military services are testing SAF as part of energy security and emissions reduction goals.
These early adopters are paying premium prices, essentially subsidizing the development of the industry. As production scales up, costs should decrease, making SAF accessible to more airlines and routes.
The Road Ahead: What Needs to Happen
For SAF to become more than a niche product, several pieces need to fall into place:
Policy support: Government incentives, mandates, and carbon pricing can help level the playing field between SAF and conventional fuel. Europe is implementing mandates requiring increasing percentages of SAF use over time. Similar policies elsewhere could accelerate adoption.
Technology advancement: Continued research into more efficient production methods, new feedstocks (like algae grown in saltwater), and improved conversion processes can reduce costs and increase supply.
Infrastructure investment: Building out the production facilities, collection networks, and distribution systems needed to supply SAF at scale requires significant capital investment—estimated in the tens of billions of dollars globally.
Certification expansion: Getting more SAF pathways certified for higher blend ratios or 100% use would maximize the benefit of available supply.
Consumer awareness: Flying is often essential—for seeing family, doing business, or experiencing the world. SAF offers travelers a way to reduce the climate impact of necessary flights. But it requires awareness and often a willingness to pay a premium.
Beyond Carbon: The Other Emissions
While carbon dioxide gets most of the attention, aircraft also produce other emissions that affect the climate:
Nitrogen oxides (NOx): These contribute to ozone formation and have climate warming effects, though regional and short-lived compared to CO₂.
Particulate matter: Soot and other particles from combustion affect air quality and have climate impacts.
Contrails: Those white trails behind jets are ice crystals that can trap heat in the atmosphere, potentially contributing as much to warming as aircraft CO₂ emissions.
Interestingly, some SAF formulations produce fewer particulate emissions than conventional fuel, potentially reducing contrail formation. This suggests SAF’s climate benefits might be even greater than the lifecycle carbon numbers indicate—though more research is needed.
Alternative Futures: SAF’s Role in a Bigger Picture
Sustainable aviation fuel isn’t the only technology aiming to clean up flying:
Hydrogen aircraft: Burning hydrogen produces only water vapor. But hydrogen is bulky even when liquefied, limiting range, and requires completely redesigned aircraft and airport infrastructure.
Electric aircraft: Viable for short hops with small planes, but unlikely for long-haul large aircraft anytime soon due to battery weight.
Improved efficiency: Better aerodynamics, lighter materials, and more efficient engines can reduce fuel consumption regardless of fuel type.
SAF’s strength is that it works now, with existing aircraft, filling a gap while longer-term solutions develop. It’s not necessarily the final answer, but it’s an answer we can deploy today.
The Consumer Connection: Flight Shame and Climate Anxiety
The rise of SAF is partly driven by changing social attitudes toward flying. “Flight shame” (flygskam in Swedish, where the term originated) reflects growing awareness of aviation’s climate impact and discomfort with contributing to emissions.
For many people, flying isn’t frivolous—it’s how they see family, do their jobs, or experience cultural exchange. SAF offers a way to continue these important connections while reducing environmental harm. It’s not perfect, and it doesn’t absolve us of considering whether every flight is necessary. But it provides a path forward that doesn’t require ending air travel altogether.
The Bigger Picture: Closing the Carbon Loop
At its core, sustainable aviation fuel represents an attempt to close the carbon loop—to create a circular system where the carbon we release was recently captured rather than dug up from ancient deposits.
This concept extends beyond aviation. We’re seeing similar thinking in sustainable diesel, sustainable marine fuels, and even sustainable plastics. The underlying principle is the same: instead of a linear system (extract → use → discard), we’re building circular systems (grow/capture → use → regrow/recapture).
SAF is one piece of that puzzle, addressing one of the harder pieces—high-energy-density liquid fuels for applications where batteries don’t yet work. As we build out this circular economy, lessons from SAF production and use will inform how we decarbonize other sectors.
What It All Means
Sustainable aviation fuel won’t single-handedly solve climate change, and it faces real challenges around cost, scale, and sustainability of feedstocks. But it represents something important: a pragmatic solution that works with existing infrastructure while we develop longer-term technologies.
The beauty of SAF is that it turns waste into value. That used cooking oil from your local restaurant? It could help power a flight across the Pacific. Agricultural residues that would otherwise decompose in fields? Jet fuel. Carbon dioxide pulled from the air using renewable energy? A closed-loop fuel that lets us fly without adding to atmospheric carbon.
We’re not there yet. SAF is still expensive, still limited in supply, still requiring policy support to compete with conventional fuel. But the trajectory is clear: as we scale up production, improve processes, and invest in infrastructure, sustainable aviation fuel will play an increasing role in keeping the world connected while protecting the planet.
Looking Forward
The next decade will be crucial for SAF. With major airlines committing to its use, governments implementing supportive policies, and producers scaling up operations, we’ll see whether this technology can transition from niche to mainstream.
For aviation to achieve net-zero emissions by 2050—the industry’s stated goal—SAF will need to supply a large percentage of fuel demand, complemented by efficiency improvements, emerging technologies like hydrogen for some routes, and potentially carbon offsets for remaining emissions.
It’s an ambitious target. But consider that the entire aviation industry—millions of flights connecting billions of people—was built in less than a century. The shift to sustainable fuels is complex, but not impossible.
The next time you board a flight, you might wonder what’s in the fuel tanks. Increasingly, the answer might include a blend of conventional jet fuel and sustainable alternatives made from sources as varied as cooking oil, forest residues, or even the CO₂ captured from the air.
It’s not a perfect solution, and the journey to truly sustainable aviation will be long. But it’s a start—a pragmatic, deployable technology that works with the aircraft we have, not just the aircraft we wish we had. And in the challenge of cleaning up our skies, pragmatic solutions that work today are exactly what we need.