Problems at several California oil refineries have choked the supply of gasoline, again driving up prices, but an expert expects the higher cost to be temporary.

Patrick DeHaan, senior petroleum analyst for gasbuddy.com, said gas inventories in California are almost at a 20-year low because of the refineries’ drop in production.

That has driven up prices. A month ago, the average cost for a gallon of regular in Santa Rosa was $4.235. It fell to $4.19 a week ago, but was back up to $4.236 on Friday, according to AAA.

DeHaan said he expects the price pressures to ease in a week or two as the refineries’ production increases. But don’t expect big drops in prices. And prices may rise a bit more before easing.

He said his company is expecting gas prices to range from $4.10 to $4.40 a gallon across the state by July 4, “perhaps on the lower end of the range.”

On Friday, AAA said San Francisco had the highest average price for gas at $4.335, while Yuba City was the lowest at $4.148. The state average was $4.253. Hawaii had the highest average at $4.557, while South Carolina was the lowest at $3.459.

A reason California’s prices are higher than many other states is that refineries must brew a special formulated gas to meet the state’s air pollution rules.

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