SAN DIEGO — The average price of a gallon of self-serve regular gasoline in San Diego County rose on Thursday to its highest amount since July 21, 2015, rising 2.5 cents to $4.186.

The average price has increased 54.3 cents over the past 17 days, including 5.4 cents on Wednesday, according to figures from the AAA and Oil Price Information Service. It is 34.1 cents more than one week ago, 55.5 cents higher than one month ago, and 37.3 cents greater than one year ago. It has risen 84.5 cents since the start of the year.

The rising prices are the result of diminished supply primarily caused by unplanned maintenance issues at the Chevron and Marathon refineries in Los Angeles County and the absence of imported gasoline, according to Jeffrey Spring, the Automobile Club of Southern California's corporate communications manager.

The lack of imports means area refineries do not have some ingredients needed to make the summer blend of gasoline, contributing to the diminished supply, said Marie Montgomery, a public relations specialist with the Automobile Club of Southern California.

Stations in most areas of Southern California are required to continue selling summer blend gasoline until Oct. 31.

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