KILLDEER, N.D. -- Dustin Bergsing was 21 and six weeks a father when he arrived here at Marathon Oil Corp.'s Buffalo 34-12H well pad, a square of red gravel carved into a low hill. By dawn, he was dead. A co-worker found him shortly after midnight, slumped below the open hatch of a tank of Bakken Shale crude oil. It was Bergsing's job to pop the hatch and record how much was inside. An autopsy found he died of "hydrocarbon poisoning due to inhalation of petroleum vapors."