The US oil rig count fell by seven this week to 638, according to the driller Baker Hughes.

Last week, the oil rig count climbed for a second straight period, by five.

Last week marked the first back-to-back climb this year, preceded by 25 weeks of declines. That led some in the industry to think the rig count may have bottomed, including the CEO of Schlumberger, the world's biggest oilfield-services provider.

In the second-quarter earnings statement released Thursday, Paal Kibsgaard said: "We believe that the North American rig count may now be touching the bottom, and that a slow increase in both land drilling and completion activity could occur in the second half of the year."

Morgan Stanley had forecast, based on historical patterns, that the rig count would bottom approximately 25 weeks from when producers started taking rigs offline. We are now past that period.

Oil prices rebounded from mid-April through June and breached $60 a barrel, a near where Morgan Stanley analysts said producers would be comfortable with ramping up production, which has remained fairly high amid the rig-count plunge.

Prices have slid since then, and crude oil is headed for a third straight week of declines. Oil dipped after news of the Iran nuclear deal crossed, as there are concerns that the lifting of sanctions will boost Iranian oil in an already oversupplied market.

Following the data release on rig counts, West Texas Intermediate crude-oil futures were near flat, near $50.80 a barrel.