California-blend gasoline in Los Angeles weakened for a second day against futures after Tesoro Corp. (TSO) was said to start a hydrotreater at the Los Angeles refinery that was shut for maintenance.

Tesoro’s 97,000-barrel-a-day Los Angeles refinery started the hydrotreater, which removes sulfur and other impurities from refined oil products, over the weekend after a week of planned work, a person familiar with the plant’s operations said today. Tina Barbee, a Tesoro spokeswoman at the company’s headquarters, didn’t immediately return an e-mailed request for comment.

California-blend gasoline, or Carbob, in Los Angeles dropped 1.5 cents to a premium of 53.5 cents a gallon against futures traded on the New York Mercantile Exchange, according to data compiled by Bloomberg. Prompt delivery fell 5.68 cents to $3.494 a gallon.

San Francisco Carbob declined 2 cents against gasoline futures to a premium of 56.5 cents a gallon.

Conventional, 87-octane gasoline in Portland, Oregon, a benchmark for the U.S. Northwest, fell 1.5 cents to a premium of 69.5 cents a gallon.

BP Plc (BP/) plans to restore service to a crude unit at the 234,000-barrel-a-day Cherry Point refinery in Washington state by early this week, two people familiar with the schedule said May 10. Initial efforts to start the unit May 8 failed when an upset forced the refinery to shut it again, the two people said.

To contact the reporter on this story: Lynn Doan in San Francisco at ldoan6@bloomberg.net

To contact the editor responsible for this story: Dan Stets at dstets@bloomberg.net