GREET (Greenhouse gases, Regulated Emissions, Energy use in Transportation)

GREET (Greenhouse gases, Regulated Emissions, and Energy use in Transportation) is a lifecycle greenhouse-gas accounting model maintained by Argonne National Laboratory under sponsorship from the U.S. Department of Energy. GREET produces the lifecycle carbon- intensity (CI) factors used as the basis for fuel CI calculations in California's LCFS, Oregon's CFP, Washington's CFS, and the U.S. federal Section 45Z Clean Fuel Production Credit.

Model structure

GREET is structured as two coupled modules:

• GREET 1 — fuel-cycle (well-to-wheels) emissions accounting for transportation fuels, covering production, processing, transport, and combustion stages
• GREET 2 — vehicle-cycle emissions accounting for vehicle manufacturing, including powertrain and battery manufacturing emissions for electrified vehicles

For LCFS, CFP, CFS, and Section 45Z, GREET 1 is the relevant module — fuels are evaluated on their well-to-wheels emissions. The vehicle cycle is treated separately in those programs.

Annual update cycle

Argonne releases an updated GREET model annually, typically in October of each year. The update incorporates the latest energy and feedstock data, refined emission factors for petroleum and natural gas, updated electricity-grid emission factors by NERC subregion, and revisions to the feedstock-specific land-use-change factors based on the most recent peer-reviewed literature. The annual release is posted on the Argonne National Laboratory GREET website.

Regulator-modified versions

While Argonne's annual GREET is the upstream reference, regulators adopt their own modified versions for use in compliance:

• CA-GREET 3.0 — CARB's California-specific version, with CA grid mix, CA feedstock supply, and CA-specific transport distances. CARB pathway petitions submitted under LCFS are scored against CA-GREET 3.0
• OR-GREET — Oregon DEQ's CFP version with Oregon-specific grid mix
• WA-GREET — Washington Ecology's CFS version
• 45Z-GREET — the Treasury-approved version of GREET fixed by IRS notice for each Section 45Z compliance year

The regulator-modified versions diverge from Argonne's upstream model in narrow but important ways: regional electricity-grid mix, regional feedstock supply curves, and specific land-use-change methodologies.

Coverage of pathways

A typical GREET pathway has the following input categories:

• Feedstock — crop or waste source (soybean oil, used cooking oil, corn starch, sugarcane, etc.)
• Process configuration — combined heat and power, natural-gas-fired boiler, electric boiler, biomass-fired boiler
• Hydrogen source — for hydrotreating pathways (steam methane reforming vs renewable hydrogen)
• Co-product allocation — energy-content vs market-value vs displacement methods for assigning emissions to a process's co-products
• Transport modes and distances

Each input category contributes to the fuel's gCO2e/MJ score.

Indirect land-use change handling

GREET's treatment of indirect land-use change (ILUC) is one of the most analyzed elements. The U.S. Department of Energy's GREET maintains ILUC factors based on the GTAP-BIO-AEZ economic model maintained at Purdue University. Regulator-specific versions can adjust the ILUC factors based on policy choices about model uncertainty.

Historical context

The GREET model was first released by Argonne in 1996. Over its history, the model has expanded from gasoline and diesel coverage to include biodiesel, renewable diesel, hydrogen, ethanol pathways, sustainable aviation fuel, and electrified vehicle pathways. Each program rulemaking that adopts GREET as the CI calibration source includes a regulatory hold on the specific GREET version used — program rules don't auto-update when Argonne releases its annual upstream version.

Co-product allocation methodology

Co-product allocation is a notable methodological choice in any GREET pathway. When a process produces fuel as one of several outputs (e.g., soy biodiesel produces glycerin as a co-product, corn ethanol produces distillers grains), GREET allows several allocation methods. The most common are:

• Energy-content allocation — divides the process's emissions among co-products in proportion to their energy content
• Market-value allocation — divides emissions in proportion to market value of each co-product
• Displacement allocation — gives the co-product an emissions credit equal to the emissions of the conventional product it is assumed to displace

CARB's CA-GREET 3.0 uses energy-content allocation by default, while some other jurisdictions adopt market-value allocation. The choice can move a fuel's CI score by several gCO2e/MJ.

Sources

Modeling: GREET model documentation, Argonne National Laboratory (anl.gov/es/greet). California: CA-GREET 3.0 documentation maintained by CARB. ILUC: GTAP-BIO-AEZ model, Purdue University Center for Global Trade Analysis. Section 45Z: IRS Notice 2025-10 and related guidance. LCFS pathway certifications: 17 CCR 95488. The Argonne GREET annual update notes are posted on the GREET website.