HOUSTON, Dec. 8 (Xinhua) -- The number of active drilling rigs in the United States increased to 626 this week, up by one from the previous week but down by 154 from last year, according to the weekly data released by Houston-based oilfield services company Baker Hughes on Friday.
These active drilling rigs included 503 oil rigs operating in U.S. oil fields, down by two from the previous week; 119 gas rigs, up by three; and four miscellaneous rigs, down by one.
The rigs included 605 land drilling rigs and 21 offshore drilling rigs.
Of them, 52 were directional drilling rigs, 559 were horizontal drilling rigs and 15 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.