U.S. oil drillers collectively sent 12 more rigs into the patch this week, the Houston oilfield services company Baker Hughes reported Friday. Gas drillers added one rig.

The rise was driven again by drillers in West Texas' Permian Basin.

The total rig count rose to 637, up from a low of 404 in May. The count still lags the same period last year, when 709 drilling rigs were operating in U.S. oil and gas fields.

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The number of active oil rigs jumped to 510 this week. Gas rigs ticked up to 126. The number offshore again stagnated at 22, down 2 year over year.

Total rig counts lifted by 14 in Texas, two in New Mexico and one in Colorado. North Dakota lost one, Oklahoma and Wyoming two.

The Permian, which straddles Texas and New Mexico, added 12 rigs. No other U.S. oilfield added more than one.

Drilling activity has followed the modest rebound in prices, from February's low of about $26 a barrel to more than $50 in recent weeks.

Prices settled on Thursday at $50.90.