Five-second answer
Claim we investigated
Ecology's final regulatory analysis estimated the cap-and-invest regulations would increase retail transportation fuel prices by 1-3%.
Inaccurate: the measured increase has been several times larger. Before cap-and-invest began on January 1, 2023, Ecology's final regulatory analysis estimated that it would raise retail transportation fuel prices by 1-3%, or roughly 4.5 to 14 cents a gallon at 2023 Washington prices. A difference-in-differences comparison of weekly EIA prices finds a Washington-specific premium of 41.6 cents in 2023, 24.2 in 2024, 46.1 in 2025 and 44.4 in 2026 (January 2024 dollars, vs. seven states). The premium rose and fell with allowance auction prices quarter by quarter, with a slope of about 1.0.
One-minute summary
What the evidence establishes
- Ecology's September 2022 final regulatory analysis estimated a 1-3% increase in retail transportation fuel prices. At Washington's 2023 average price of about $4.53 (January 2024 dollars), that is about 4.5 to 13.6 cents a gallon.
- Against seven EIA states without fuel carbon pricing, Washington's gas-tax-adjusted premium over its 2015-2022 relationship was 41.6 cents in 2023, 24.2 in 2024, 46.1 in 2025, and 44.4 in January-October 2026.
- Against the U.S. average, the Rocky Mountain region and Colorado, the 2025 premium was 41 to 56 cents. California, which has its own carbon market, is the only comparison with small effects (3 to 19 cents).
- As a share of the Washington pump price, the 7-state premium was about 9% in 2023, 6% in 2024, 12% in 2025 and 10% in 2026.
- Quarter by quarter, the premium tracked the auction-implied carbon cost per gallon: both averaged about 39 cents, and the regression slope is about 1.0. Both fell in 2024 when allowance prices collapsed during the repeal campaign.
- The state's own consultant (Greene Economics, in Ecology Pub. 26-14-043) estimated 36 to 51 cents for 2023 and 24 cents for 2024. This analysis reproduces those figures within 6 cents for EIA-based comparisons.
- At Ecology's own primary-scenario allowance price of $58.31, the carbon cost of a gallon of E10 gasoline is about 46 cents (FactHub arithmetic). The 1-3% estimate implied that most of that cost would not reach drivers; the measured data indicate it did.
The evidence
The conclusion rests on the combined record. Expand each item to see its role and limitations.
| Method | Institution / country | Year(s) | What it shows | Key limitation | Primary links |
|---|---|---|---|---|---|
| Difference-in-differences on weekly EIA retail regular gasoline prices, January 2015 to October 2026, in January 2024 dollars. Washington prices are normalized to a constant 49.4-cent state gas tax so the 2025 and 2026 tax increases are excluded. Effect = mean weekly Washington-minus-comparison gap in each year minus the 2015-2022 mean gap. Newey-West standard errors with 12 lags. | U.S. Energy Information Administration, Bureau of Labor Statistics, FactHub United States | 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023, 2024, 2025, 2026 | Against seven states without fuel carbon pricing (CO, TX, FL, MN, OH, NY, MA), the premium was 41.6 cents in 2023 (standard error 12.0), 24.2 in 2024 (4.9), 46.1 in 2025 (6.1) and 44.4 in 2026 through October 5 (4.2). Against the U.S. average, the Rocky Mountain region and Colorado, every year from 2023 to 2026 is between 20 and 56 cents. A shorter 2019-2022 baseline changes results by under 6 cents. | The method measures every Washington-specific change relative to the comparison states, not only the Climate Commitment Act; the Clean Fuel Standard (under 1 cent by Ecology's estimate), refinery outages and other local shocks are included. Placebo tests with a fictitious 2019 start show single-year deviations of up to about 21 cents, so any single year is approximate. Oregon, the closest supply-chain comparison, has no EIA weekly series. | U.S. Energy Information Administration FactHub |
| Carbon cost per gallon = quarterly auction settlement price x EPA emission factor for E10 gasoline (8.78 kg CO2 per gallon x 0.90 fossil share = 7.902 kg). Compared quarter by quarter with the measured premium; ordinary least squares slope of premium on carbon cost. | Washington Department of Ecology, U.S. Environmental Protection Agency, U.S. Energy Information Administration, FactHub United States | 2023, 2024, 2025, 2026 | Across 2023Q1-2026Q3 the measured premium averaged 38.7 cents and the carbon cost 38.9 cents. The slope of premium on carbon cost is 1.03 against the seven states and 1.02 against the U.S. average. When allowance prices fell from about $52 to $26 in early 2024 while a repeal initiative was pending, the premium fell too; both rose again in 2025. A cost that moves one-for-one with the allowance price is what full pass-through of the program's compliance cost would produce. | Fifteen quarters is a small sample, and correlation (0.62 against the seven states) is descriptive. 2023Q1 shows almost no premium, possibly because compliance costs had not yet reached retail prices. Six of the fifteen auction prices come from secondary reports that cite Ecology results. | Washington Department of Ecology U.S. Environmental Protection Agency FactHub |
| FactHub compared its estimates with Table 2 of Ecology Pub. 26-14-043 (Clean Fuel Standard 2024 progress report), which reports Greene Economics' difference-in-differences estimates for 2023 and 2024. | Washington Department of Ecology, Greene Economics, FactHub United States | 2023, 2024 | The consultant estimated 51.4 cents (AAA U.S. average comparison) and 36.0 cents (EIA all-state fixed effects) for 2023, and 24 cents for 2024 under both comparisons. FactHub's corresponding EIA-based estimates are 39.7 and 41.6 for 2023 and 20.2 and 24.2 for 2024. A state-commissioned analysis therefore also found an effect several times the 1-3% estimate. | The consultant's study and this analysis use the same basic method and some of the same data, so they are not fully independent. The consultant used AAA prices for some comparisons; FactHub used EIA throughout. | Washington Department of Ecology FactHub |
| Compared the 1-3% range in Ecology's final regulatory analysis (Pub. 22-02-047, Table 78, as cited in Ecology's September 2023 letter) with the measured premium divided by the annual average Washington price. | Washington Department of Ecology, U.S. Energy Information Administration, FactHub United States | 2022, 2023, 2024, 2025, 2026 | Washington averaged $4.53 a gallon in 2023, $4.02 in 2024, $3.97 in 2025 and $4.59 in 2026 (January 2024 dollars). The 7-state premium equals about 9.2%, 6.0%, 11.6% and 9.7% of those prices, two to four times the top of the 1-3% range. Ecology's primary scenario assumed a $58.31 allowance in 2023, which at full pass-through implies about 46 cents a gallon; the measured effect is consistent with that cost reaching drivers. | Converting a percent estimate into cents depends on the assumed pump price. FactHub used the measured Washington average in January 2024 dollars; Ecology's own conversion is not reproduced here. The percent figures below are FactHub arithmetic from the dataset's effects and EIA's Washington average, not a separately saved analysis. | Washington Department of Ecology Washington Department of Ecology (Director Laura Watson) U.S. Energy Information Administration |
| Quarterly carbon cost per gallon (allowance method) or measured gasoline premium (measured method) multiplied by taxed on-road gallons from the Transportation Revenue Forecast Council. | Washington Transportation Revenue Forecast Council, FactHub United States | 2023, 2024, 2025, 2026 | From 2023 through 2026Q3 the two methods agree within 1% for gasoline: about $3.8 billion ($3,808 million by the allowance method and $3,790 million by the measured-premium method). Including on-road diesel, the allowance method gives about $5.1 billion. | Gallon volumes for fiscal years 2026-2027 are state forecasts. Diesel figures assume no renewable blending and are upper bounds; there is no measured diesel premium because EIA publishes no weekly Washington diesel series. These are costs to fuel buyers, not state revenue. | Washington Transportation Revenue Forecast Council FactHub |
2. 2. The premium rose and fell with allowance auction prices
Across 2023Q1-2026Q3 the measured premium averaged 38.7 cents and the carbon cost 38.9 cents. The slope of premium on carbon cost is 1.03 against the seven states and 1.02 against the U.S. average. When allowance prices fell from about $52 to $26 in early 2024 while a repeal initiative was pending, the premium fell too; both rose again in 2025. A cost that moves one-for-one with the allowance price is what full pass-through of the program's compliance cost would produce.
Limit: Fifteen quarters is a small sample, and correlation (0.62 against the seven states) is descriptive. 2023Q1 shows almost no premium, possibly because compliance costs had not yet reached retail prices. Six of the fifteen auction prices come from secondary reports that cite Ecology results.
Verify: Auction #15 Summary Report, September 2026 (Pub. 26-14-063) 40 CFR Part 98 Subpart MM, Table MM-1 Washington Gasoline Price Premium and Carbon Allowance Costs, 2015-2026
3. 3. The state's own consultant measured a similar premium
The consultant estimated 51.4 cents (AAA U.S. average comparison) and 36.0 cents (EIA all-state fixed effects) for 2023, and 24 cents for 2024 under both comparisons. FactHub's corresponding EIA-based estimates are 39.7 and 41.6 for 2023 and 20.2 and 24.2 for 2024. A state-commissioned analysis therefore also found an effect several times the 1-3% estimate.
Limit: The consultant's study and this analysis use the same basic method and some of the same data, so they are not fully independent. The consultant used AAA prices for some comparisons; FactHub used EIA throughout.
Verify: Clean Fuel Standard 2024 Progress (Pub. 26-14-043), Table 2 Washington Gasoline Price Premium and Carbon Allowance Costs, 2015-2026
4. 4. Ecology's 1-3% estimate was well below the measured effect in every full year
Washington averaged $4.53 a gallon in 2023, $4.02 in 2024, $3.97 in 2025 and $4.59 in 2026 (January 2024 dollars). The 7-state premium equals about 9.2%, 6.0%, 11.6% and 9.7% of those prices, two to four times the top of the 1-3% range. Ecology's primary scenario assumed a $58.31 allowance in 2023, which at full pass-through implies about 46 cents a gallon; the measured effect is consistent with that cost reaching drivers.
Limit: Converting a percent estimate into cents depends on the assumed pump price. FactHub used the measured Washington average in January 2024 dollars; Ecology's own conversion is not reproduced here. The percent figures below are FactHub arithmetic from the dataset's effects and EIA's Washington average, not a separately saved analysis.
Verify: Final Regulatory Analyses for Chapter 173-446 WAC, Climate Commitment Act Program (Pub. 22-02-047) Letter to Sen. Shelly Short re: Cap and Invest Program Allowance Prices, September 21, 2023 Weekly retail gasoline and diesel prices
5. 5. The added cost is in the billions of dollars
From 2023 through 2026Q3 the two methods agree within 1% for gasoline: about $3.8 billion ($3,808 million by the allowance method and $3,790 million by the measured-premium method). Including on-road diesel, the allowance method gives about $5.1 billion.
Limit: Gallon volumes for fiscal years 2026-2027 are state forecasts. Diesel figures assume no renewable blending and are upper bounds; there is no measured diesel premium because EIA publishes no weekly Washington diesel series. These are costs to fuel buyers, not state revenue.
Verify: February 2026 Transportation Economic and Revenue Forecasts, Vol. II, Table A.1 Washington Gasoline Price Premium and Carbon Allowance Costs, 2015-2026
Common questions
“Ecology showed that Oregon prices rose almost as much in 2023, so the program can't be responsible.”
The letter compared raw price changes between January and August 2023 (Washington up $1.27, Oregon up $1.03), with no pre-program baseline and in a period of strong seasonal increases. That comparison cannot separate a persistent premium from shared seasonal movement. EIA publishes no weekly Oregon series, so this analysis cannot test Oregon directly; it is the most important missing comparison. Even taken at face value, the 24-cent difference in the letter is above 1-3% of the price.
“Washington gas has always been expensive; the premium is just the usual gap.”
The method subtracts each comparison region's 2015-2022 average gap, so the usual Washington premium is removed. What remains is the change since 2023. Placebo runs with a fictitious 2019 start produce deviations up to about 21 cents in single years, smaller than the 2023, 2025 and 2026 effects and averaging near zero.
“Refinery outages and oil companies, not the carbon program, raised prices.”
Local supply shocks are included in the measured premium, which is why this article does not claim the whole premium is the program. But the premium moved with the allowance price quarter by quarter, including the 2024 drop when allowances fell by half, which an unrelated refinery shock would not be expected to do.
“The 2025 gas-tax increase explains the recent premium.”
Washington prices are normalized to a constant 49.4-cent state tax before comparison, so the 6-cent July 2025 increase and the July 2026 adjustment are removed.
“The program is worth the cost.”
This article measures the price effect against the state's estimate. It does not weigh emissions reductions, revenue uses, or rebates, which are separate questions.
Conclusion
Several independent lines agree that the Climate Commitment Act's effect on Washington gasoline prices has been far larger than the 1-3% Ecology estimated before the program began. The measured Washington premium is 24 to 46 cents a gallon in each year from 2023 to 2026 against seven states, and similar against other comparison regions. It equals about 6 to 12% of the pump price. It follows auction prices quarter by quarter with a slope near one, and the state's own consultant found similar numbers for 2023 and 2024. The gap appears to come from pass-through, not the allowance price: Ecology's own primary scenario assumed a $58 allowance, which works out to about 46 cents of carbon cost per gallon, close to what drivers paid. What remains uncertain is the exact size in any one year, because the method cannot fully separate the program from other Washington-specific shocks, and Oregon, the best comparison, has no weekly federal price series. The finding concerns the size of the price effect only; it says nothing about whether the program's benefits justify the cost.
How we checked
- Defined the claim narrowly as Ecology's published estimate of the program's effect on retail transportation fuel prices (1-3%), not broader claims about the program's value.
- Obtained the estimate from Ecology's September 2023 letter to Sen. Shelly Short, which cites Table 78 of the September 2022 final regulatory analysis (Pub. 22-02-047).
- Built the FactHub dataset from EIA weekly retail gasoline prices for Washington and comparison regions, CPI-U from FRED, the Washington gas-tax schedule, Ecology auction results and TRFC fuel volumes.
- Estimated annual and quarterly difference-in-differences effects against five comparison regions, with placebo and baseline-sensitivity checks.
- Compared quarterly effects with auction-implied carbon cost and checked the results against the state consultant's published estimates.
- Recorded limitations, including the missing Oregon series, secondary sources for six auction prices, and the inability to isolate the program from other Washington-specific shocks.
Editorial note: Scope: This article evaluates the size of the program's effect on gasoline prices against Ecology's estimate. It does not evaluate emissions effects, revenue uses or the program's overall merit. External review: No external economist or energy-market specialist has reviewed this article. To verify yourself: (1) open the cited FactHub dataset and compare its annual and quarterly analyses with the EIA series; (2) read Ecology's September 2023 letter and Table 78 of Pub. 22-02-047; (3) compare with Table 2 of Ecology Pub. 26-14-043; (4) submit counter-evidence through the challenge form. Challenge this fact-check: Identify the specific conclusion you dispute and provide verifiable evidence that could change it. Credible challenges deserve review and a visible response.
Expert-review status
No external specialist review has been recorded for this article.
Funding and conflicts
Funding: No external funding was received for this article or the underlying dataset.
Ownership: FactHub prepared the curated data, analysis and article. Original data remain attributable to EIA, BLS, Ecology, EPA and TRFC.
Conflicts: No financial conflict has been identified. FactHub has no affiliation with fuel suppliers, the Department of Ecology, or campaigns for or against Initiative 2117.
Sources
Sources are labeled by their role so readers can evaluate the evidence independently.
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The estimate under test
Washington Department of Ecology.
Final Regulatory Analyses for Chapter 173-446 WAC, Climate Commitment Act Program (Pub. 22-02-047)
Identifier: Ecology Pub. 22-02-047, Table 78
September 2022 cost-benefit analysis for the adopted rule; the source of the 1-3% retail fuel-price estimate and the $58.31 primary-scenario allowance price.
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Claim provenance
Washington Department of Ecology (Director Laura Watson).
Letter to Sen. Shelly Short re: Cap and Invest Program Allowance Prices, September 21, 2023
Restates the 1-3% estimate, the $58.31 allowance assumption and the Oregon comparison. The copy is hosted by the Washington Policy Center, which opposes the program; the letter itself is on Ecology letterhead.
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State-commissioned estimate (replication)
Washington Department of Ecology.
Clean Fuel Standard 2024 Progress (Pub. 26-14-043), Table 2
Greene Economics' difference-in-differences estimates of the Washington-specific gas price change for 2023 and 2024.
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Principal price data
U.S. Energy Information Administration.
Weekly retail gasoline and diesel prices
Weekly retail regular gasoline prices for Washington and the comparison regions.
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Allowance prices
Washington Department of Ecology.
Auction #15 Summary Report, September 2026 (Pub. 26-14-063)
Most recent auction settlement price; earlier auction sources are listed in the dataset.
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Emission factors
U.S. Environmental Protection Agency.
40 CFR Part 98 Subpart MM, Table MM-1
CO2 per gallon for gasoline and diesel, used to convert allowance prices to cents per gallon.
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Fuel volumes
Washington Transportation Revenue Forecast Council.
February 2026 Transportation Economic and Revenue Forecasts, Vol. II, Table A.1
Taxed gasoline and diesel gallons by fiscal year.
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Curated data and saved analyses
FactHub.
Washington Gasoline Price Premium and Carbon Allowance Costs, 2015-2026
All tables, saved analyses, limitations and reproduction scripts for the numbers in this article.
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FactHub dataset
Washington Gasoline Price Premium and Carbon Allowance Costs, 2015-2026
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Tables: annual-effects, weekly-prices
Annual difference-in-differences effects by comparison region
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Tables: quarterly-comparison, auction-prices
Quarterly premium vs. carbon cost: slope and correlation
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Tables: annual-effects
Comparison with the Ecology consultant's 2023-2024 estimates
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Tables: weekly-prices
Placebo test with a fictitious 2019 start
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Tables: cost-estimates, fuel-gallons
Estimated cost to on-road fuel users
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- FactHub chart wa-cca-premium-vs-carbon-cost
Update history
- Initial version.
Challenge this fact-check
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