D6 RIN

A D6 RIN is the Renewable Identification Number assigned to a gallon of conventional renewable fuel produced or imported into the United States under the federal Renewable Fuel Standard (RFS). In practice, the D6 pool is dominated by corn-starch ethanol, which is the conventional renewable fuel whose pathway is approved under 40 CFR 80.1426. D6 also covers a small set of grandfathered ethanol facilities that pre-date the program's greenhouse-gas threshold requirements.

D6 in the nesting hierarchy

The RFS is structured as a nested hierarchy of four D-codes. From most specific to most general: D3 (cellulosic biofuel), D4 (biomass-based diesel), D5 (advanced biofuel) and D6 (conventional renewable fuel). The nesting rule under 40 CFR 80.1427 means that a higher-tier RIN can satisfy a lower-tier obligation but not the reverse. A D4 RIN can be retired against a D6 obligation; a D6 RIN cannot satisfy a D4, D5, or D3 obligation. This one-way nesting is why the D6 price floor has historically tracked the conventional-renewable RVO and why the D4–D6 spread is a standing data point in program analysis.

Equivalence values for ethanol

A D6 RIN represents one ethanol-equivalent gallon. Because corn-starch ethanol has the same energy content as the program's ethanol baseline, each gallon of qualifying ethanol generates one D6 RIN per 40 CFR 80.1415. The post-2027 EV regime change does not affect D6 generation; ethanol's 1.0 multiplier is unchanged.

RIN generation, transfer and retirement

D6 RINs are created in the EPA Moderated Transaction System (EMTS) when a producer or importer reports a qualifying batch with the appropriate production-pathway pointer. They follow the same generation–transfer– retirement lifecycle as other D-codes: assigned RINs accompany the physical gallon until separation, after which they trade freely. Retired RINs are credited against an obligated party's RVO at year-end compliance filing. Annual compliance reports are due 31 March under 40 CFR 80.1451.

RVO and the conventional category

The Renewable Volume Obligation is set annually by EPA in the Federal Register. The conventional-renewable obligation has historically been calibrated near the statutory 15-billion-gallon ethanol cap; the multi-year RFS Set Rule (Federal Register vol. 88, 27 July 2023) confirmed the conventional category at 15.0 billion gallons through the 2023–2025 compliance years. Where annual ethanol blending falls short of the conventional RVO, obligated parties cover the gap through D4 or D5 RIN retirements (the nesting rule allows higher-tier RINs to "fill" the D6 shortfall) or through small-refinery exemptions and waiver actions described elsewhere in this glossary.

Historical drivers

D6 prices reflect the gap between physical ethanol blending capacity, the E10 blendwall (~10% of gasoline volume), and the annual RVO. Documented historical drivers include: the 2017–2019 SRE wave (small-refinery exemptions reducing demand), the 2020 COVID-19 demand contraction, the post-2022 expansion of renewable diesel into the D4 pool that compressed the D6–D4 spread, the rollback and re-finalization of 2020–2022 volumes in the December 2022 EPA RFS rule, and the OBBBA July 2025 provisions modifying the Section 45Z Clean Fuel Production Credit timeline. Public EMTS aggregates show that the D6 weekly volume-weighted average price has historically tracked far below the D4 price because the conventional category lacks the structural undersupply that drives the biomass-based diesel category.

Sources

EPA RFS regulations are codified at 40 CFR Part 80, Subpart M. Key sections: equivalence values (40 CFR 80.1415), RIN generation (40 CFR 80.1426), separation (40 CFR 80.1473), nesting and obligation discharge (40 CFR 80.1427), compliance filing (40 CFR 80.1451). The 2023 multi-year Set Rule was published at 88 FR 44468 (27 July 2023). Aggregated weekly RIN data are published on the EPA "RIN Trades and Price Information" page; record-level transactions remain confidential business information per 40 CFR 80.1454.