Across 15 quarters, Washington's gasoline premium over a 7-state comparison group averaged 38.7 cents per gallon, nearly identical to the average carbon cost implied by allowance auctions (38.9 cents). Both fell sharply in 2024, when allowance prices collapsed while a repeal initiative was pending, and rose again in 2025. A regression slope of about 1.0 is consistent with drivers paying essentially the full carbon cost, though the premium also reflects other Washington-specific factors.
| cents_per_gallon_jan2024 | quarter_start | series |
|---|---|---|
| 39.4 | 2023-01-01 | Carbon cost |
| 1.6 | 2023-01-01 | WA premium |
| 45.2 | 2023-04-01 | Carbon cost |
| 44.2 | 2023-04-01 | WA premium |
| 50.4 | 2023-07-01 | Carbon cost |
| 64.5 | 2023-07-01 | WA premium |
| 41.2 | 2023-10-01 | Carbon cost |
| 56.1 | 2023-10-01 | WA premium |
| 20.3 | 2024-01-01 | Carbon cost |
| 23.9 | 2024-01-01 | WA premium |
| 23.4 | 2024-04-01 | Carbon cost |
| 40.4 | 2024-04-01 | WA premium |
| 23.3 | 2024-07-01 | Carbon cost |
| 11.9 | 2024-07-01 | WA premium |
| 31.1 | 2024-10-01 | Carbon cost |
| 21.4 | 2024-10-01 | WA premium |
| 38.3 | 2025-01-01 | Carbon cost |
| 26.5 | 2025-01-01 | WA premium |
| 44.7 | 2025-04-01 | Carbon cost |
| 50.9 | 2025-04-01 | WA premium |
| 48.7 | 2025-07-01 | Carbon cost |
| 57.4 | 2025-07-01 | WA premium |
| 53.3 | 2025-10-01 | Carbon cost |
| 49.6 | 2025-10-01 | WA premium |
| 48.8 | 2026-01-01 | Carbon cost |
| 41 | 2026-01-01 | WA premium |
| 47.3 | 2026-04-01 | Carbon cost |
| 53.3 | 2026-04-01 | WA premium |
| 28.9 | 2026-07-01 | Carbon cost |
| 38.5 | 2026-07-01 | WA premium |