SAN DIEGO, CA — The average price of a gallon of self-serve regular gasoline in San Diego County rose three-tenths of a cent Friday to $4.189 after the largest weekly increase in four years pushed it to its highest amount since July 21, 2015.

The average price has increased 54.6 cents over the past 18 days, including 2.5 cents on Thursday, according to figures from the AAA and Oil Price Information Service. It is 27.9 cents more than one week ago, 54.8 cents higher than one month ago, and 36.7 cents greater than one year ago. It has risen 84.8 cents since the start of the year.

Gas prices began increasing rapidly last month after Saudi Arabia oil production facilities were attacked, and the increases sharpened after three Los Angeles-area refineries slowed or halted production due to maintenance issues and no imported gasoline was available to make up for the shortfall, according to Jeffrey Spring, the Automobile Club of Southern California’s corporate communications manager.

Local refineries had already cut back production of summer blend gasoline in anticipation of switching to selling the winter blend beginning Nov. 1, creating even more of a shortage.

“The good news is that Los Angeles wholesale gasoline prices have dropped sharply in the last two days after refiners began selling off gasoline and there are indications that refinery production problems are ending,” Spring said.