Washington held its fourth cap-and-trade auction Aug. 30, putting more than 8.5 million carbon allowances up for bid and potentially boosting both state revenues and fuel prices.

The Department of Ecology will announce auction results Sept. 6. The three previous auctions, including a special auction triggered by high allowance prices, brought in $919.5 million.

Ecology will hold at least one more auction this year, on Dec. 6. Since cap-and-trade took effect Jan. 1, Washington gas prices have risen more than twice as much as the U.S. average, according to prices reported by the U.S. Energy Information Administration.

High fuel costs combined with high labor costs are pinching producers, Washington State Dairy Federation policy director Jay Gordon said Thursday.

“This is reaching crisis proportions,” he said. “We have farmers heading for the exit.”

Washington lawmakers modeled cap-and-trade after California’s decade-old program. The states, however, are far apart on the cost of allowances, the driver of both state revenue and fuel prices.

Allowances sold for $35.20 each in August at the California-Quebec cap-and-trade auction, according to the California Air Resources Board.

The price was an all-time high for California, but it was still lower than in Washington, where allowances have sold for between $48.50 and $66.68 in the first three auctions.

The Western States Petroleum Association estimated in July that cap-and-trade was adding 50 cents to a gallon of gasoline in Washington, compared to 26 cents in California.

The petroleum association plans to update its estimate after Ecology announces auction results next week, a spokesman said.

Oil companies and natural gas companies must acquire one allowance for every ton of carbon their products emit. Cap-and-trade auctions are also open to investors who anticipate allowances will increase in value.

The auctions have been competitive. Investors bought more than 10% of the allowances sold at the last regular auction. Allowance prices were high enough to trigger a special auction closed to investors.

Ecology received 12.79 bids per allowance as companies apparently sought to take advantage of the absence of investors to get allowances at the pre-set price of $51.90.

Washington’s allowance prices could diverge further from California’s. Washington will reduce the cap on allowances by 7% a year, doubling California’s pace in reducing carbon emissions from fossil fuels.

The petroleum association warned the rapid reduction in the number of allowances could push up fuel costs. The pace is necessary to halve greenhouse gas emissions by 2030, according to Ecology.

Since the start of the year, the average cost of regular unleaded gasoline has increased by $1.27 in Washington, compared to 89 cents in California and 59 cents nationwide, according to EIA.

Average U.S. gas prices heading into Labor Day weekend are 16 cents a gallon lower than last year, but are 38 cents higher in Washington, the largest year-over-year increase in the country.

Washington gas prices a year ago were slightly lower than in Oregon, but on Thursday were 34 cents higher, according to AAA.

Washington and California are the only states where regular unleaded topped $5 a gallon Thursday. Washington, California and Hawaii were the only states where diesel topped $5.50 a gallon.