The number of rigs actively exploring for oil and natural gas in the United States increased by 11 this week to 1,739.

Of the rigs running nationwide, 1,442 were exploring for natural gas and 291 for oil, Houston-based Baker Hughes Inc. reported Friday. Baker Hughes listed six as miscellaneous.

A year ago, the rig count stood at 1,474.

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.

Of the major oil- and gas-producing states, Oklahoma gained eight rigs, Colorado gained three and California gained one. Wyoming lost seven rigs and Louisiana lost three. Alaska, New Mexico and Texas were unchanged.