After three fiery accidents involving trains carrying crude oil out of North Dakota's Bakken Shale, regulators and industry officials are trying to figure out why the oil is exploding.
Crude is flammable, but before being refined into products such as gasoline it is rarely implicated in explosions.
Yet earlier this week, when a BNSF Railway Co. train hauling 104 tank cars filled with Bakken crude struck another train, some of the cars exploded one after the other, releasing fireballs that blazed several stories above the frozen prairie.
"Crude oil doesn't explode like that," said Matthew Goitia, chief executive of Peaker Energy Group LLC, a Houston company that is developing crude-by-rail terminals.
The blast in Casselton, N.D., 25 miles west of Fargo, is just the latest explosion involving crude pumped out of the Bakken. Federal investigators and railroad and energy-company officials are probing whether additives to the oil or mislabeling of the liquid contributed to the series of explosions.