April 1 The number of rigs drilling for oil and natural gas in the United States fell for the 15th straight week to the lowest level since at least 1940, data showed on Friday, as the energy price rout takes its toll on shale producers' financing and their ability to drill new wells. Drillers cut 14 oil and gas rigs in the week to April 1, bringing the total rig count down to 450, oil services company Baker Hughes Inc said in its closely followed report.