MOSES LAKE — Diesel prices in Washington reached a record high over the weekend, even as gasoline prices remained largely unchanged, according to AAA data released Monday.

The average price of diesel in Washington climbed to $7.43 per gallon Sept. 21, up 21 cents a week ago and more than $1.12 higher than a month ago. AAA reported diesel reached an all-time state record of $7.45 per gallon on Sept. 20.

By comparison, the average price of regular gasoline in Washington was $5.57 per gallon Monday, just 1 cent higher than a week ago. However, regular gasoline prices remain 32 cents above a month ago and 95 cents higher than a year ago.

The trend is similar in Grant and Adams counties, where regular gasoline prices have remained relatively steady over the past several weeks. Grant County's average price was $5.46 per gallon Monday, unchanged from last week, while Adams County's average was $5.44, down 4 cents a week earlier.

Both counties remain slightly below the statewide average, but well above national prices.

Nationally, regular gasoline averaged $4.48 per gallon Monday, up 16 cents a week ago. Diesel averaged $6.51 per gallon, an increase of 28 cents from last week and 93 cents from a month ago.

Washington drivers are paying about $1.09 more per gallon for regular gasoline than the national average. According to the Washington Dept. of Revenue, motorists in state pay 74.9 cents per gallon in state and federal fuel taxes before other costs are added.

While gasoline prices have moved only modestly in recent weeks, diesel has seen a sharp increase across the country.

“Average gasoline prices rose in virtually every state over the last week, with 45 states seeing increases of more than 3 cents per gallon, led by the Great Lakes region where refinery issues sent Michigan, Indiana, Illinois, Ohio, and Wisconsin all up more than 30 cents per gallon,” said Patrick De Haan, head of petroleum analysis at GasBuddy. “Diesel rose in every state, with five states seeing increases exceeding 50 cents per gallon, as continued strikes on Russian oil refineries tighten global diesel supply, a pressure further amplified in the Great Lakes by regional refinery issues. Any broader directional change will depend heavily on overseas developments, and with new Houthi attacks and fresh U.S.-Iran escalations, the outlook remains deeply uncertain.”

Washington diesel prices have risen dramatically throughout September. The statewide average stood at $6.31 per gallon a month ago and $5.07 a year ago. Monday's average of $7.43 represents a month-over-month increase of nearly 18% and a year-over-year increase of more than 46%.

Gasoline prices have also climbed significantly during 2026. The statewide average price for regular gasoline was $3.83 per gallon in January. Prices rose steadily through the spring, peaked at an average monthly price of $5.74 in May, eased during the summer, and have since climbed back to $5.57.

In Grant County, regular gasoline prices fluctuated within a narrow range during September, moving from $5.47 per gallon Sept. 8 to $5.46 on Sept. 21. Adams County prices have fallen from $5.55 per gallon Sept. 8 to $5.44.

Despite the recent stability at local pumps, the record-high diesel prices could add costs for trucking companies, farmers and other industries that rely heavily on diesel-powered equipment heading into the fall harvest season.