OLYMPIA — Once the Legislature adjourns, Washington gasoline and diesel prices will rise two ways — suddenly, then gradually.

House Democrats approved April 24 raising the per-gallon tax by 6 cents on gasoline and 9 cents on diesel beginning July 1, with more yearly increases to come. Senate Democrats passed a similar tax increase, though some differences must be resolved.

House and Senate Democrats also have passed and sent to Gov. Bob Ferguson a bill requiring oil companies to blend in more biofuels. The petroleum industry estimates the bill will add up to 25 cents a gallon to fuel by 2028.

Washington already has the third-highest fuel prices in the U.S., according to AAA. Washington has one of the higher fuel taxes in the country at 49.4 cents a gallon. Cap-and-trade is adding 44 cents a gallon, the Western States Petroleum Association estimates.

The petroleum association said Washington policies increase fuel prices by $1 a gallon, compared to 50 cents in Oregon, Idaho and Montana.

“The costs are starting to add up. I think it’s really important you, legislators, look at that carefully,” the association’s Northwest vice president Jessica Spiegel told the Senate Environment and Energy Committee in April.

The gasoline and diesel tax increases headlined the House tax package to fund transportation. The package passed, 51-47. All Republicans voted “no,” as did seven Democrats.

The package has a slew of other new or higher taxes, including on tires, vehicles, driver’s licenses, vehicle registrations, title transfers, car rentals, electric bicycles and “luxury” motor homes.

“Mind-boggling,” said Thurston County Rep. Andrew Barkis, the top-ranking Republican on the House Transportation Committee. “This is a potpourri of taxes. There are so many taxes in here.”

Transportation Committee Chairman Jake Fey, D-Tacoma, said the state needs the money to keep up with the escalating cost of transportation projects.

“Raising taxes, I don’t believe, is fun for any of us,” Fey said.

The gasoline tax will automatically increase by 2% a year beginning in 2026, under the House plan. Until now, lawmakers have had to vote for each increase.

“It’s better for people. It’s more predictable,” Rep. Sharon Wylie, D-Vancouver, said.

The diesel tax, until now the same as the gas tax, will go up another 3 cents in 2027 and then automatically increase 2% a year. Democrats said pollution from diesel was particularly harmful.

Republicans complained Democrats were taxing diesel at a higher rate than gasoline.

“Diesel is the working man’s fuel. It’s what gets the work done,” said Rep. Mary Dye, R-Pomeroy.

Fuel prices likely will gradually rise because of House Bill 1409, which puts the state on a more aggressive path to reduce carbon emissions from gasoline and diesel.

Under existing law, oil companies must gradually reduce emissions from their products by 20% by 2038. HB 1409 ramps up the reductions to at least 45% and as much as 55%.

Democrats said the bill will stimulate biofuel production. Republicans said the bill will help Midwest farmers and ethanol makers, but Washington farmers will reap only higher fuel costs.

“The problem is feedstock. To be able to make these biofuels, you have to have corn. Washington is a corn deficient state,” said Republican Sen. Perry Dozier, an Eastern Washington wheat farmer. “This is another nail in the coffin for agriculture.”