* Deal will make Tesoro second-largest Calif. refiner
* BP Arco station owners told sale could happen by June 1
* Antitrust approval could come as early as Friday -source (Adds refining capacities, no comment from Calif. AG)
By Erwin Seba and Diane Bartz
HOUSTON/WASHINGTON, May 16 (Reuters) - Independent westernU.S. refiner Tesoro Corp may take ownership of BP Plc's 240,000 barrel per day (bpd) refinery in Carson,California, as early as June 1, sources familiar with thetransaction said on Thursday.
Other sources told Reuters that the U.S. Federal TradeCommission, which assessed the deal to ensure that it compliedwith antitrust law, is prepared to approve the purchase withindays.
That approval could come as early as Friday, said one sourcewith knowledge of discussions between the company and theagency. It was not known if the FTC will place conditions on thedeal's approval.
The sources could not speak for attribution, citing the needto protect business relationships. A BP spokesman declined todiscuss the transaction.
Tesoro announced last August that it had agreed to buy BP'sCarson plant for $2.5 billion. The proposed deal has beenawaiting approval by the FTC and by California's attorneygeneral.
The sale includes an 800-station retail network anddistribution and storage assets.
Assuming the Carson refinery purchase is approved by the FTCwithout conditions, Tesoro would become the second-largestrefiner in California after Chevron Corp. California isthe largest gasoline market in the United States.
Adding the Carson refinery to Tesoro's other two Californiarefineries would give Tesoro a combined crude oil throughput of 509,800 bpd, or 26 percent of the state's refining capacity,according to data published by the U.S. Energy InformationAdministration.
Chevron's two California refineries have a combinedthroughout of 521,271 bpd, or 26.7 percent of the state's crudeoil refining capacity.
In recent days, owners of BP Arco-branded retail stations inCalifornia have been told to expect a change to Tesoro as earlyas the first day of June. "June 1, that's the date for Tesoro totake over," one of the sources said.
Once the transaction is cleared, BP's U.S. downstreamoperation will be solely focused on refineries in the northerncontinental United States, where cheaper Canadian crude oil iseasily obtained.
A Tesoro spokeswoman declined to discuss the status of thedeal.
"As previously communicated, we expect the transaction toclose before mid-2013," said Tina Barbee, who declined toelaborate.
An FTC spokesman declined on Thursday to discuss the statusof the commission's review of the transaction. On May 2, TesoroChief Executive Greg Goff said the company was near the end ofthe regulatory review process.
A spokeswoman for California Attorney General Kamala Harrisdeclined to comment on the pending sale.
In addition to the refinery and retail network, the saleincludes more than 100 miles of pipeline, three marineterminals, four land storage terminals and four productmarketing terminals.
Tesoro plans to sell the distribution and storage assets toits master limited partnership, Tesoro Logistics LP,for about $1 billion, within a year of closing.
Tesoro also intends to combine operations of the Carsonrefinery with its 103,800 bpd refinery in Wilmington,California. The two refineries nearly abut each other in the LosAngeles industrial suburbs north of the port of Long Beach.
BP in 2011 announced plans to sell the Carson refinery aswell as its Texas City, Texas, refinery. Marathon Oil Corp purchased the Texas refinery in February as part of a$2.4 billion deal that includes terminals, pipelines and otherassets. (Reporting by Erwin Seba in Houston and Diane Bartz inWashington; Editing by Gerald E. McCormick, Tim Dobbyn, MatthewLewis and Steve Orlofsky)