The number of operating oil and natural gas rigs in the United States went down by 7 to 1,993 this week, according to a weekly report released here on Friday.A total of 1,132 rigs were exploring for oil and 856 for natural gas in the U.S., with another five rigs listed as miscellaneous, according to the report released by the Houston- based oil service company Baker Hughes Inc..The rig count stood at 1,713 a year ago.Of the leading oil- and gas-producing states, Oklahoma and North Dakota added one rig each.Texas and Colorado lost four rigs each, while Louisianna lost two. New Mexico and Pennsylvania lost one rig respectively.The Baker Hughes rig counts, first issued in 1944, serve as an important business barometer for drilling firms and their suppliers to gauge the overall business environment of the oil and gas industry.The U.S. rig count peaked at 4,530 in 1981 as a result of the oil boom. It plummeted to a record low of 488 in 1999.