D3 RIN

A D3 RIN is the Renewable Identification Number assigned to a gallon of cellulosic biofuel produced or imported under the U.S. Renewable Fuel Standard (RFS). Cellulosic biofuel is the most stringent category in the program, defined under 40 CFR 80.1401 as biofuel derived from cellulose, hemicellulose, or lignin and meeting a 60% lifecycle greenhouse-gas reduction threshold relative to a 2005 petroleum baseline.

Eligible D3 pathways

Approved D3 pathways under 40 CFR 80.1426 have historically been dominated by biogas-derived renewable natural gas (RNG) from landfill, agricultural digester, and wastewater-treatment-plant sources. The agricultural digester segment has expanded materially since 2018 as dairy-manure RNG projects have come online. Other approved D3 pathways include cellulosic ethanol from corn-stover and other lignocellulosic feedstocks (a much smaller share of historical generation), and cellulosic gasoline streams that meet the 40 CFR 80.1416 pathway definitions.

Why D3 dominates the cellulosic pool with RNG

Although the original RFS2 framework (Energy Independence and Security Act of 2007) anticipated cellulosic ethanol as the dominant D3 pathway, the technology curve for liquid cellulosic ethanol stalled. EPA's 2014 RNG-as-D3 rulemaking (79 FR 42128, 18 July 2014) opened the cellulosic category to compressed and liquefied biogas used as transportation fuel, which has since become the principal source of D3 generation. Public EMTS aggregates published on EPA's RIN Trades and Price Information page show the share of D3 RINs from RNG well above 95% in recent years.

Equivalence values

A D3 RIN is one ethanol-equivalent gallon. EVs are set in 40 CFR 80.1415:

• Cellulosic ethanol — 1.0 RINs per gallon
• Cellulosic gasoline blendstocks — 1.0 RINs per gallon
• Renewable compressed natural gas (CNG) and liquefied natural gas (LNG) — 77,000 BTU per RIN, applied per the regulation's energy-content formula

The 2027 EV regime change applies to biomass-based diesel and renewable diesel; D3 ethanol-equivalent multipliers are unchanged.

Cellulosic waiver credits

When the realised cellulosic supply falls short of the annual cellulosic RVO, EPA may issue cellulosic waiver credits (CWCs) under 40 CFR 80.1456. The CWC price is set in the Federal Register each year using the formula in section 211(o)(7)(D)(ii) of the Clean Air Act, indexed to the higher of $0.25 or a fuel-cost-based offset. Obligated parties may purchase CWCs and pair them with a D5 RIN to discharge the cellulosic obligation.

Outlier band on D3 prices

Public D3 weekly volume-weighted average prices have historically spanned a wider band than D4 or D6 because the cellulosic pool is thinner and CWC issuance can compress trading activity. The EPA-published D3 outlier filter applies a $0.05–$3.50 per-RIN band across the full history, distinct from the D4/D6 $0.05–$3.00 post-2019 band. Charts should annotate the outlier band as published.

Historical drivers

D3 generation rose sharply after the 2014 RNG rule, then accelerated after 2018 as dairy-digester projects scaled. The 2023 multi-year Set Rule (88 FR 44468, 27 July 2023) established multi-year cellulosic volumes through the 2023–2025 compliance years. The OBBBA July 2025 law modified the Section 45Z Clean Fuel Production Credit framework, which indirectly affects the economics of D3-eligible RNG projects through the lifecycle-emissions accounting at 26 USC 45Z(b).

Outstanding rulemakings

EPA continues to issue pathway petitions for novel cellulosic streams, including pyrolysis-oil-to-diesel pathways and lignin-to-fuel routes. Each pathway petition must demonstrate the 60% lifecycle GHG threshold using the EPA's GREET-derived emissions factors and the carbon-intensity methodology in the 2010 RFS2 rulemaking (75 FR 14670, 26 March 2010). A new pathway becomes part of the regulatory text only after notice and comment rulemaking concludes.

Sources

EPA RFS regulations: 40 CFR 80.1401 (definitions), 40 CFR 80.1415 (EVs), 40 CFR 80.1426 (generation), 40 CFR 80.1456 (CWCs). The 2014 RNG-as-D3 rulemaking is at 79 FR 42128. The 2023 multi-year Set Rule is at 88 FR 44468. D3 weekly aggregates are on the EPA RIN Trades and Price Information page.