Sensitivity: 2019-2022 baseline

What this dataset measures

Official state analysis of the Climate Commitment Act's gas-price effect stops at 2024. This release extends the same method through 2026 using public federal data and links the measured premium to auction prices.

Geography

Washington State, United States (comparison regions)

Unit of observation

One EIA survey week for prices; one quarter for auctions; one fiscal year for fuel volumes.

Update cadence

Immutable research release; new data requires a new version.

Curator

FactHub Research Team

Supporting files

Source snapshots, manifests, quality reports, documentation, and other materials used to produce or review this release.

• source-manifest.json Source manifest · application/json · 4.7 KB (4,794 bytes)

  URLs, retrieval date, byte lengths, and SHA-256 digests of retrieved EIA and FRED source files.

• README.md Documentation · text/markdown · 1.5 KB (1,553 bytes)

  Method and reproduction instructions.

• quality-report.md Quality report · text/markdown · 986 bytes

  Validation results and data-quality notes.

• did.js Transformation manifest · text/javascript · 9.7 KB (9,903 bytes)

  Difference-in-differences analysis (Node.js 20).

• passthrough.js Transformation manifest · text/javascript · 3.2 KB (3,231 bytes)

  Quarterly pass-through comparison.

• cost.js Transformation manifest · text/javascript · 5.1 KB (5,229 bytes)

  Cost estimates.

• build_release.js Transformation manifest · text/javascript · 36.2 KB (37,105 bytes)

  Builds release tables and this payload.

Saved analyses

Sources

1. U.S. Energy Information Administration, weekly retail gasoline prices Principal source of weekly prices for Washington and comparison regions.

   Retrieved October 9, 2026. U.S. federal government data. Retrieved files are identified by digest in source-manifest.json; curated values redistributed with attribution to EIA.

2. BLS CPI-U (CPIAUCSL) via Federal Reserve Bank of St. Louis FRED Inflation adjustment.

   Retrieved October 9, 2026. U.S. federal government data. Factor values redistributed with attribution.

3. EPA 40 CFR Part 98 Subpart MM, Table MM-1 default factors CO2 emission factors for gasoline (8.78 kg/gal) and diesel (10.21 kg/gal).

   Retrieved October 9, 2026. U.S. federal regulation. Linked as a public record; source bytes are not redistributed in this release.

4. Washington Transportation Revenue Forecast Council, Feb 2026 forecast, Vol. II, Table A.1 Taxed gasoline and diesel gallons by fiscal year.

   Retrieved October 9, 2026. Washington State public record. Linked as a public record; source bytes are not redistributed in this release.

5. Washington Dept. of Ecology, Clean Fuel Standard 2024 Progress (Pub. 26-14-043), Table 2 State-commissioned 2023-2024 estimates used in replication-check.

   Retrieved October 9, 2026. Washington State public record. Linked as a public record; source bytes are not redistributed in this release.

6. Ecology, Cap-and-Invest Auction Revenue Forecast Summary, Nov 2023 2023Q1-Q3 settlement prices.

   Retrieved October 9, 2026. Washington State public record. Linked as a public record; source bytes are not redistributed in this release.

7. Ecology, Auction #4 Summary Report, Dec 2023 2023Q4 settlement price.

   Retrieved October 9, 2026. Washington State public record. Linked as a public record; source bytes are not redistributed in this release.

8. S&P Global Commodity Insights, Washington auction prices drop sharply (Mar 2024) 2024Q1 settlement price (secondary).

   Retrieved October 9, 2026. News report. Linked as a public record; source bytes are not redistributed in this release.

9. Ecology Revenue Forecast Summary June 2024 (copy hosted by Washington Research Council) 2024Q2 settlement price (secondary host).

   Retrieved October 9, 2026. Washington State public record. Linked as a public record; source bytes are not redistributed in this release.

10. Ecology, Auction #7 Summary Report, Sep 2024 2024Q3 settlement price.

    Retrieved October 9, 2026. Washington State public record. Linked as a public record; source bytes are not redistributed in this release.

11. Environmental Defense Fund, Climate 411, Mar 12 2025 2024Q4 and 2025Q1 settlement prices (secondary).

    Retrieved October 9, 2026. Advocacy blog. Linked as a public record; source bytes are not redistributed in this release.

12. Ecology, Auction #10 Summary Report, Jun 2025 2025Q2 settlement price.

    Retrieved October 9, 2026. Washington State public record. Linked as a public record; source bytes are not redistributed in this release.

13. Ecology news release, Sep 10 2025 2025Q3 settlement price.

    Retrieved October 9, 2026. Washington State public record. Linked as a public record; source bytes are not redistributed in this release.

14. Ecology, Auction #12 Summary Report, Dec 2025 2025Q4 settlement price.

    Retrieved October 9, 2026. Washington State public record. Linked as a public record; source bytes are not redistributed in this release.

15. Environmental Defense Fund, Climate 411, Mar 11 2026 2026Q1 settlement price (secondary).

    Retrieved October 9, 2026. Advocacy blog. Linked as a public record; source bytes are not redistributed in this release.

16. Environmental Defense Fund, Climate 411, Jun 10 2026 2026Q2 settlement price (secondary).

    Retrieved October 9, 2026. Advocacy blog. Linked as a public record; source bytes are not redistributed in this release.

17. Ecology, Auction #15 Summary Report, Sep 2026 (Pub. 26-14-063) 2026Q3 settlement price ($39.50, auction held 2026-09-02).

    Retrieved October 9, 2026. Washington State public record. Linked as a public record; source bytes are not redistributed in this release.

18. Washington Legislature, ESSB 5987 (2015), session law Enacted 7-cent (Aug 1 2015) and 4.9-cent (Jul 1 2016) increases from a 37.5-cent base to 49.4 cents.

    Retrieved October 9, 2026. Washington State public record. Linked as a public record; source bytes are not redistributed in this release.

19. OPB, Washington gas tax increase July 1 2025 July 2025 increase from 49.4 to 55.4 cents.

    Retrieved October 9, 2026. News report. Linked as a public record; source bytes are not redistributed in this release.

20. Washington State Standard, gas tax inflation adjustment July 2026 adjustment to about 56.5 cents.

    Retrieved October 9, 2026. News report. Linked as a public record; source bytes are not redistributed in this release.

Limitations and reproducibility

Fully reproducible from public EIA and FRED downloads with Node.js 20 and no packages.: source-manifest.json lists every retrieved file with URL and SHA-256. The four scripts regenerate every table and this payload.

• Difference-in-differences estimates capture all Washington-specific factors, not only the Climate Commitment Act; the Clean Fuel Standard (under 1 cent per gallon by Ecology's estimate), refinery outages, and other state-specific shocks are included.
• Placebo tests show single-year pre-policy deviations of up to about 20 cents per gallon, so any one year's estimate is approximate; HAC standard errors understate that uncertainty.
• EIA publishes no weekly Oregon or Idaho series; Oregon, the closest supply-chain comparison, is absent. Idaho is represented only within PADD 4.
• Prices are statewide averages and do not show regional variation within Washington.
• Six of fifteen auction prices come from secondary reports citing Ecology results.
• Cost estimates use taxed on-road gallons only and assume E10 gasoline; diesel estimates are upper bounds.
• Descriptive comparisons do not by themselves establish causation; the quarterly link to auction prices is supporting, not conclusive, evidence.