July 28, 2014 at 11:00 pm

Survey: U.S. gas prices fall 9 cents to $3.58

Bustling refineries driving down costs beyond Mich.

Photo of Shell gas station in St. Clair Shores on Monday. Gasoline prices in Michigan dropped about 14 cents in the last week alone, the fourth straight week they've fallen. (David Coates / The Detroit News)

U.S. refineries are flexing their muscles and helping lower gasoline prices in the middle of the peak driving season.

The average price for regular gasoline at U.S. pumps dropped 9.04 cents in the two weeks ended July 25 to $3.5795 a gallon, according to Lundberg Survey Inc., based on information obtained from about 2,500 filling stations.

Prices are 9.51 cents lower than a year ago and are at the lowest level since March 21, the survey showed.

In Michigan, the news is even better: Gasoline prices in the state dropped about 14 cents in the last week alone, the fourth straight week they’ve fallen.

AAA Michigan said Monday the average price of a gallon of self-serve regular unleaded gasoline was $3.49 on Sunday. That’s about 17 cents less than one year ago.

Dearborn-based AAA Michigan surveys fuel costs at 2,800 Michigan gas stations daily. It said the cheapest price was $3.39 a gallon in the Lansing-East Lansing area and the most expensive was $3.68 in the Marquette area.

Retail prices declined nationwide as refineries processed the most petroleum in government records dating to 1989 in the week ended July 11. Plants in the Midwest exceeded their nameplate capacity during that week.

“It’s really a mid-summer gift,” Trilby Lundberg, the president of California-based Lundberg Survey, said in a telephone interview. “Refiners have been on a kick to run more crude, run at high rates and to cut price.”

The highest price for gasoline in the lower 48 states among the markets surveyed was in San Francisco, at $4.03 a gallon, Lundberg said. The lowest price was in Tulsa, Okla., where customers paid an average of $3.23. Regular gasoline averaged $3.83 on Long Island, N.Y., and $3.96 in Los Angeles.

Refineries processed 16.81 million barrels a day in the week ended July 18, just off the highs reached the prior week, Energy Information Administration data show.

Plants are taking advantage of the U.S. shale boom, which has raised oil production 65 percent in the past five years. The increased output has pushed the settlement price of U.S. benchmark West Texas Intermediate futures below European Brent every day since Aug. 17, 2010.