HOUSTON, April 19 -- The number of active drilling rigs in the United States decreased to 619 this week, up by two from the previous week but down by 134 from this time last year, according to the weekly data released by Houston-based oilfield services company Baker Hughes on Friday.

These active drilling rigs included 511 oil rigs operating in U.S. oil fields, up by five from the previous week; 106 gas rigs, down by three; and two miscellaneous rigs, unchanged from last week.

The rigs included 599 land drilling rigs, zero inland water drilling rigs, and 20 offshore drilling rigs.

Of them, 50 were directional drilling rigs, 555 were horizontal drilling rigs and 14 were vertical drilling rigs.

So far, the Permian Basin in western Texas and eastern New Mexico has been the largest source of shale oil production growth in the United States, having become an engine of supply growth outside the Organization of the Petroleum Exporting Countries in the past years.

  - Xinhua