The Mechanics of Sustainable Aviation Fuel: How Airlines Are Decarbonizing Flight

The aviation industry faces a fundamental physics problem: current battery technologies are simply too heavy to power long-haul commercial flights, yet the sector is under immense global pressure to decarbonize its operations. The solution currently dominating industry strategy and investment is Sustainable Aviation Fuel (SAF), a drop-in replacement for conventional Jet-A kerosene that requires zero modifications to existing aircraft engines or airport fueling infrastructure.

Unlike conventional jet fuel, which pulls carbon from deep underground and releases it into the atmosphere, SAF is produced from renewable feedstocks. Because these feedstocks—ranging from agricultural waste to used cooking oil—absorbed carbon dioxide during their lifecycle, the net addition of greenhouse gases is drastically lower.[1]

When evaluated on a full lifecycle basis, Sustainable Aviation Fuel can reduce carbon emissions by up to 80% compared to traditional fossil fuels, making it the primary lever in the aviation sector's commitment to reach net-zero emissions by 2050. The mechanics of SAF rely entirely on its chemical identicality to conventional jet fuel.

Once refined, it is blended with traditional kerosene—currently approved for up to a 50% ratio—and pumped directly into the same fuel tanks and jet engines that have powered commercial flight for decades. This seamless integration allows airlines to begin decarbonizing immediately without waiting for revolutionary new aircraft designs.[1]

The most commercially mature method for producing this fuel is the Hydroprocessed Esters and Fatty Acids (HEFA) pathway. This process takes lipid-based feedstocks, such as animal fats and used cooking oil, and uses hydrogen to remove the oxygen molecules. During the HEFA process, the resulting straight paraffinic molecules are cracked and isomerized to match the exact carbon chain length required for jet fuel. Because it utilizes existing refinery technologies and established chemical processes, HEFA is currently the most cost-effective and widely deployed production method in the world.

However, the HEFA pathway faces a fundamental limitation: global feedstock availability. There is simply not enough used cooking oil and waste animal fat in the world to replace the billions of gallons of jet fuel consumed annually by commercial airlines. To scale beyond waste oils, the industry is aggressively developing the Alcohol-to-Jet (AtJ) pathway.

This method converts alcohols, such as ethanol derived from corn, sugarcane, or agricultural waste, into jet fuel by removing oxygen and linking the molecules together through a process called oligomerization. While AtJ opens up a vastly larger feedstock pool, it introduces complex debates around land use and the diversion of agricultural resources away from food production.

The ultimate endgame for sustainable aviation is the Power-to-Liquid (PtL) pathway, often referred to as synthetic e-fuels. This highly advanced process captures carbon dioxide directly from the atmosphere or industrial exhaust and synthesizes it with green hydrogen produced via renewable electricity. PtL fuels offer the promise of near-infinite scalability without competing for agricultural land or relying on waste streams. However, the technology remains highly energy-intensive and currently costs several times more than conventional jet fuel, requiring massive investments in renewable energy infrastructure to become economically viable.[2]

Because SAF production is currently concentrated in a few specialized facilities globally, physically transporting the fuel to every airport worldwide would generate unnecessary emissions and logistical bottlenecks. To solve this inefficiency, the industry utilizes a "book and claim" accounting system.

Under this model, SAF is pumped into the fuel supply at an airport near the production facility, displacing conventional fossil fuel in that specific location. An airline operating on the other side of the world can then pay the price premium for that SAF, claiming the environmental attributes for its own corporate sustainability targets, even if its physical aircraft are burning traditional kerosene.

This decoupling of the physical fuel from its environmental attributes allows capital to flow into SAF production facilities regardless of their geographic location, accelerating the industry's overall transition. By treating the global aviation fuel supply as a single interconnected pool, book and claim ensures that every drop of SAF produced immediately contributes to decarbonization, without the carbon penalty of shipping the fuel across oceans.

It provides the financial mechanism necessary for airlines to fund the green premium of SAF while operating at airports that do not yet have physical access to the blended product.

Despite the technological viability of these pathways and accounting systems, the sheer scale of the challenge remains daunting. In 2024, global SAF production reached approximately 1 million tonnes, which represents just 0.3% of total global jet fuel consumption. The International Air Transport Association (IATA) estimates that SAF will need to account for roughly 65% of the emissions reductions required to hit the 2050 net-zero target. Achieving that scale will require a massive mobilization of capital, government incentives, and a rapid transition from feedstock-constrained HEFA production to infinitely scalable synthetic e-fuels.[1][2]