The number of rigs actively exploring for oil and natural gas in the United States rose by 15 this week to 1,901.

Of the rigs running nationwide, 1,504 were exploring for natural gas and 389 for oil, Houston-based Baker Hughes Inc. reported Friday. Eight were listed as miscellaneous.

A year ago, the rig count stood at 1,773.

Of the major oil- and gas-producing states, Oklahoma and Wyoming each gained six rigs, New Mexico added five and Louisiana added two. Colorado lost six rigs, Texas lost two and Alaska and California each lost one rig.

Baker Hughes has tracked rig counts since 1944. The tally peaked at 4,530 in 1981, during the height of the oil boom. The industry posted several record lows in 1999, bottoming out at 488.