Crude Oil Prices Slip

Crude oil prices slipped in choppy trading on Friday and were headed for a third week of losses, amid pressure from a stronger dollar and expectations of increased exports from Iran.

The U.S. dollar was on track for its biggest weekly rise since May and traded near a seven-week high against a basket of currencies after being bolstered Thursday by lower U.S. jobless claims.

Crude futures received a brief boost from Baker Hughes Inc data showing U.S. drillers cut seven rigs this week, after adding rigs the previous two weeks.

Brent front-month September crude was down 11 cents at $56.81 a barrel at 1:36 p.m. EDT (1736 GMT), off more than 3 percent for the week and more than 10 percent for the month.

Brent's August contract expired on Thursday.

U.S. August crude, also known as West Texas Intermediate (WTI), was down 39 cents at $50.52, down more than 4 percent this week and 15 percent in July. The August contract expires on July 21.

"WTI selling is continuing off of dollar strengthening," Jim Ritterbusch, president at Ritterbusch & Associates in Galena, Illinois, said in a research note.

Iran has started to ship oil to Asia that had been stored offshore for months after Tehran and six world powers reached an agreement about Tehran's nuclear program on Tuesday, clearing the way for an easing of sanctions on Iran.

"With the Iran deal, people are aware there is more supply coming, so all impetus for a price correction higher has gone," said Hans van Cleef, senior energy economist at ABN Amro in Amsterdam.

Britain's North Sea Buzzard oilfield ramped up after an outage that started on Wednesday. The outage was supportive to Brent as oil from the field contributes to the calculation of the futures price.

U.S. RBOB gasoline futures held on to gains on Friday, supported by recent government data showing strong gasoline demand in the United States.

Thursday's news of fewer U.S. jobless claims also buoyed gasoline futures, even as a string of encouraging economic data bolstered the case for the Federal Reserve to raise interest rates, a move considered bearish for crude futures as it could curb liquidity.

Despite Friday's strength, gasoline futures were on track to post a decline of more than 5 percent for the week, the biggest since mid-March and the fifth consecutive weekly drop.

(Additional reporting by Simon Falush in London; Editing by Marguerita Choy and Bernadette Baum)