The Renewable Fuel Standard, Explained

The US Renewable Fuel Standard (RFS) sets the volume of biofuel that must be blended into American transport fuel each year. It is the largest biofuel mandate in the world, and it prices the barrel that Canadian, European and Asian buyers compete for. It is also routinely misread, because almost every number published about it is denominated in a unit that is not a gallon.

This piece sets out how the obligation is built, why the biomass-based diesel target is the wrong number to watch, and what happens at the border.

A Renewable Identification Number (RIN) is the unit of compliance. One RIN represents one ethanol-equivalent gallon. A physical gallon generates RINs in proportion to its energy content, under an equivalence value fixed in the regulation.

40 CFR 80.1415(b). Renewable natural gas is credited at 77,000 Btu per RIN; anything unlisted is calculated from its energy content.

One gallon of renewable diesel therefore creates 1.7 RINs. This is why an obligation quoted as “9.07 billion” corresponds to well under 9.07 billion gallons of fuel, and why comparing an RFS volume directly against a production statistic will mislead every time.

The standard is not one target but four, arranged as concentric circles. EPA’s final volumes for 2026 and 2027, in billions of RINs and including the reallocation of small-refinery exemptions:

EPA, Final Renewable Fuel Standards for 2026 and 2027 (27 March 2026), total applicable volumes.

Each fuel earns a RIN with a D-code, and the nesting rule is that a RIN from an inner circle satisfies every circle outside it. A biomass-based diesel RIN (D4) counts towards the diesel target, the advanced target and the total, all at once. A conventional corn-ethanol RIN (D6) reaches only the outermost.

That asymmetry is the whole economics of the program. D6 is abundant and cheap. D3 and D4 carry optionality, and are dear.

The advanced circle needs 11.10 billion RINs in 2026, and only cellulosic, biomass-based diesel and other advanced fuels can fill it. Cellulosic supplied 1.29 billion in 2025 and other advanced 0.28 billion. Biomass-based diesel is left to cover 9.53 billion RINs — against its own stated obligation of 9.07 billion.

There is a second pull. The conventional slot is the total less the advanced, or 15.71 billion RINs, and corn ethanol has to supply it. Ethanol generated 14.66 billion in 2025 and cannot easily generate more, because the market is saturated at a 10 per cent blend. The shortfall of roughly 1.05 billion RINs travels upward, and the only realistic instrument to fill it is a surplus D4.

Supply figures are 2025 RIN generation from EPA’s Moderated Transaction System. Climate Decode analysis.

Biomass-based diesel RIN generation reached 7.97 billion in 2023 and 9.18 billion in 2024, between two and three times the diesel obligation of those years. That was not oversupply. It was one fuel quietly doing the work of three obligations.

Imports generate, exports retire

RINs are created by the producer or importer, at the point fuel is made in or brought into the United States. Imported biofuel therefore generates RINs and can be used for compliance in the ordinary way.

Exports run the other way. Under section 80.1430 an exporter of renewable fuel must acquire and retire RINs equal to the exported volume multiplied by its equivalence value, within thirty days of shipment. Exporting a gallon of renewable diesel means retiring 1.7 RINs.

The logic follows from what the program is for. A gallon burned in Toronto displaces Canadian diesel, not American. If that gallon kept its RIN, a US refiner could meet its obligation with fuel that never entered the US pool, and the mandate would be satisfied on paper while domestic petroleum use was untouched. The export obligation closes that gap by cancelling the claim when the fuel leaves.

For a Canadian buyer, the consequence is direct. The RIN, the California credit and the Californian cap-at-the-rack value are all earned where the fuel is burned, and all are forfeited on export. The 45Z production credit is earned at the plant and travels with the barrel. Any Canadian policy bidding for that gallon has to replace the whole forgone use-based stack, and that netback is what sets the floor under Canadian credit prices.

EPA proposed an import RIN reduction that would have halved the RINs available to imported fuel and to fuel made from foreign feedstock. It was not finalized. In the 2026–27 rule, the agency wrote that it had concluded more time was needed, and that it intends to establish such provisions “beginning in the 2028 compliance year or shortly thereafter.”

Until that happens, it is a signal, not a constraint. It is aimed squarely at imported feedstock, and Canadian canola is among the largest single foreign inputs to US renewable diesel — which makes it worth tracking closely without yet being worth modelling as law.

Climate Decode Market Insight. Written from the regulation and EPA data: 40 CFR Part 80 Subpart M, EPA’s final Renewable Fuel Standards for 2026 and 2027, and RIN generation data from EPA’s Moderated Transaction System. Provided for information and not as investment, legal or compliance advice. © 2026 Climate Decode.