If one policy explains the size of the US biofuel industry, it is the Renewable Fuel Standard. It is the reason a town in Iowa has an ethanol plant, the reason most American gasoline is 10% ethanol, and the reason a credit called a RIN trades on commodity desks. It is also one of the most argued-over energy policies in the country. This page sets out how it actually works.
What the RFS is
The Renewable Fuel Standard (RFS) is a federal program that requires a minimum volume of renewable fuel to be blended into the United States’ transportation fuel each year. It was created by the Energy Policy Act of 2005 and then substantially expanded by the Energy Independence and Security Act of 2007 — the expanded version, with much larger volumes and a four-category structure, is usually called RFS2. The Environmental Protection Agency (EPA) administers it.
The logic is simple at the top: Congress (and now the EPA) sets national volume targets for renewable fuel; those targets are converted into obligations on the companies that supply fuel; and a credit system tracks and enforces compliance. The complexity is all in the second and third steps.
Volume obligations and RINs
Each year the EPA translates the national volume targets into a percentage — the Renewable Volume Obligation (RVO) — that applies to obligated parties, meaning refiners and importers of gasoline and diesel. An obligated party must ensure that a volume of renewable fuel equal to its RVO is blended into the supply.
It proves it did so with RINs — Renewable Identification Numbers. When a gallon of renewable fuel is produced or imported, a unique RIN is generated and attached to it. When the fuel is blended into petroleum, the RIN detaches and becomes a tradable credit. Obligated parties retire RINs to meet their obligation; those who blend more than required have surplus RINs to sell, and those who blend less must buy them. This credit market is the engine of the whole system, and RIN prices are a closely watched signal of how tight the mandate is.
The four nested categories
RFS2 does not treat all renewable fuel alike. It defines four categories, nested inside one another, each with a minimum lifecycle greenhouse-gas reduction threshold and its own RIN code:
- Total renewable fuel (D6) — the outermost volume; conventional corn-starch ethanol, meeting a 20% GHG-reduction threshold, fills most of it.
- Advanced biofuel (D5) — anything other than corn-starch ethanol achieving ≥50% GHG reduction, such as sugarcane ethanol.
- Biomass-based diesel (D4) — biodiesel and renewable diesel at ≥50% reduction.
- Cellulosic biofuel (D3) — fuels from non-food cellulosic biomass at ≥60% reduction.
Because the categories nest, a gallon of cellulosic biofuel also counts toward the advanced and total volumes. The structure was designed to pull the industry up the ladder — from conventional ethanol toward advanced and cellulosic fuels — over time.
Where the program strains
Three pressure points recur in every RFS debate. The first is the blend wall: with most fuel sold as E10 and the vehicle fleet built around it, there is a ceiling on how much ethanol the market can absorb without wider use of higher blends like E15 or E85. The second is the persistent shortfall in cellulosic volumes, which have repeatedly come in below the statutory targets because the fuels proved harder and costlier to commercialise than expected, forcing the EPA to waive volumes down. The third is small refinery exemptions, which let small refiners petition out of their obligations on hardship grounds; their use materially changes effective blending volumes and is fiercely contested by both refiners and biofuel producers.
The RFS after 2022
The 2007 statute set explicit volumes only through 2022. Beyond that, the EPA sets the annual volumes itself through rulemaking — the so-called “set” process — which hands the agency ongoing discretion over the program’s direction and makes each year’s standard a focus of lobbying and litigation. The RFS is, in that sense, no longer a fixed schedule but a continuing administrative judgement.
RFS versus low-carbon fuel standards
It is worth being clear how the RFS differs from the other major fuel policy it is often mentioned beside. The RFS is volume-based: it mandates how many gallons of renewable fuel must be blended, using GHG thresholds only to sort fuels into categories. A low-carbon fuel standard is carbon-based: it sets a falling carbon-intensity target and lets any fuel compete on its score. A fuel can be valuable under both at once — sugarcane ethanol, for instance, counts as an advanced biofuel under the RFS and earns LCFS credits for its low carbon intensity.
Related: sugarcane ethanol & the LCFS, the Open Fuel Standard, and ethanol blend levels.