The agency took oil samples from nine tank cars that were intact after the crash and subjected them to a rigorous analysis.
The samples were consistent a light, sweet crude oil, with volatility comparable to that of a condensate or gasoline product.
Crashes raise concern
Concerns about transporting oil by train were heightened after the fiery train crash, along with a string of other explosive accidents across North America, which prompted the U.S. Department of Transportation to issue an alert about the potential high volatility of crude from the Bakken oil patch.
The U.S. agency said that light crude oil from the Bakken oil region, which straddles North Dakota, Saskatchewan and Manitoba, may be different from traditional heavy crudes because it is prone to ignite at a lower temperature. The sprawling oil shale reserve is fueling the surging industry in eastern Montana and western North Dakota, which is now the second-largest U.S. oil producer behind Texas.
Experts have said that lighter crudes, which contain more natural gas, have a much lower flash point.
The amount of oil moving by rail in the U.S. has spiked since 2009, from just more than 10,000 tanker cars to a projected 400,000 cars in 2013.