Crude oil from North Dakota’s Bakken Shale formation contains several times the combustible gases as oil from elsewhere, a Wall Street Journal analysis found, raising new questions about the safety of shipping such crude by rail across the U.S. Federal investigators are trying to determine whether such vapors are responsible for recent extraordinary explosions of oil-filled railcars, including one that killed several dozen people in Canada last summer. The rapid growth of North Dakota crude-oil production—most of it carried by rail—has been at the heart of the U.S. energy boom. The volatility of the crude, however, raises concerns that more dangerous cargo is moving through the U.S. than previously believed. Neither regulators nor the industry fully has come to terms with what needs to be done to improve safety. There have been some steps, for example, slowing trains and promising to redirect around high-risk areas. But debate still rages […]