If you go to a short-order diner and ask for ham and eggs, chances are very good you’ll get less of each commodity on one plate than if you order ham or eggs separately. The same can be said for U.S. refining capacity for low-carbon renewable diesel fuel and so-called sustainable aviation fuel (SAF).

Over the past several years there has been volumes written about the potential market for SAF, and subsequent potential for North American farmers to produce feedstocks for the reduced-carbon fuel for global aviation fleets. Studies, however, show while the goals are lofty, attaining them in meaningful markets may be tricky.

In 2021 the Biden Administration announced a “grand challenge” goal of the U.S. producing 3 billion gallons of the fuel by 2030 to reduce the aviation industry’s carbon footprint in the skies. Various federal actions were initiated to support reaching the goal, including new and ongoing funding opportunities for SAF projects and fuel producers. Meanwhile, many U.S. refiners were busy overhaling their refining capacity to handle renewable diesel production through a thermal process of hydrotreating esters and fatty acids (HEFA).

To produce large volumes of SAF, additional expensive technology must be added to a renewable diesel plant either during original construction or after operations begin. The primary additional technology is a hydrocracking reactor that pre-refines hydrocarbon chains before the feedstock is sent to the distilling phase. Specifically, the reactor employs high-pressure hydrogen and special catalysts at high temperatures to shorten the long-chain hydrocarbons to meet the technical specifications for SAF.

As refiners responded to climate concerns emanating from the nation’s capital, their relatively quiet switch from predominately crude oil processing to capabilities by which to handle feedstocks ranging from soybean oil to animal fats and tallows — the processes used to produce both renewable diesel and low-carbon SAF — accounted for a steep ramp up of capacity for each distillate. Reports from the federal Energy Information Administration show in 2020 annual domestic renewable diesel refining capacity was estimated to be 800-million gallons. By the end of 2024 that figure was estimated to be 5.3 billion gallons during 2025.

Researchers in the Department of Agricultural and Consumer Economics at the University of Illinois explain while the 2025 estimates reflect a large installed-base of production capacity, there is limited information data on precisely how much of that capacity could be converted to SAF by 2026. They explain in nearly all refineries capable of producing renewable diesel, SAF also can be produced, but about 20% more feedstock is required to produce the aviation fuel rather than renewable diesel for transportation and off-road diesel fuel applications.

Also, there’s confusion in some circles as to the exact definition of Biden Administration’s 3-billion-gallon goal. In the U.S., fuel-tank-ready SAF can use low-carbon (non-petroleum) renewable jet fuel only in a 50% blend with traditional petroleum-based Jet-A. The question then arises: “Are we talking about blendable SAF or finished product ready to fuel an airliner?”

Regardless, the U of I study suggests the total renewable diesel refining capacity in the U.S. in 2025 and 2026 could range from 4.325 to 5.261 billion gallons, depending on the level of capacity that is devoted to SAF production. If SAF production is pushed to its maximum in these refineries, projected renewable diesel production capacity would be reduced by nearly 20%.

The question for 2030 then remains, are we talking about SAF in quantities sufficient to blend 3 billion gallons of fuel, or 3-billion gallons of SAF-grade blending stock. The answer could be quite telling, but as of 2025-2026 U.S. refining capacity is still far short of being able to handle the 2021 goal set out by Washington, D.C.

The U of I economists say it appears there is only one feasible pathway at present for ramping up SAF production quickly and that is to convert all or part of the production capacity of existing or soon-to-be completed renewable diesel plants.