Crude oil prices briefly rose but gave up gains after a weekly count of U.S. oil rigs fell, capping two weeks of increases.
Front-month U.S. crude futures closed down 2 cents, at $50.89 a barrel. It is down more than 4 percent this week and 15 percent in July. The August contract expires on July 21.
Brent crude was slightly higher at $57 a barrel, but off more than 3 percent for the week and about 10 percent for the month. Brent's August contract expired on Thursday.
Oilfield services firm Baker Hughes reported U.S. drillers took seven oil rigs out of fields last week, bringing the total to 638, compared with 1,554 active rigs at this time last year. The prior two weeks' gains were the first in more than seven months.