Colorado oil train derailment spills 6,500 gallons

The Union Pacific Railroad said Saturday 6,500 gallons of oil spilled after a train derailed in northern Colorado on Friday.

Cleanup operations continued into Saturday, a railroad spokeswoman said. The spill was contained to a ditch, according to a state official, preventing it from reaching the nearby South Platte River.

Out of the 100 cars caring crude oil in the train, six derailed roughly 45 miles north of Denver. The cause of the accident has yet to be determined, according to The Associated Press.

The increasing number of crude-by-rail accidents has generated debate over the best mode of transportation for crude oil.

Sen. Mark UdallMark Emery UdallSenate GOP rejects Trump’s call to go big on gun legislation Democratic primary could upend bid for Colorado seat Picking 2018 candidates pits McConnell vs. GOP groups MORE (D-Colo.) said Friday's derailment highlights the need to upgrade rail safety regulations.

Udall added that while the Transportation Department has taken steps to improve train safety, more must be done.

Despite trains carrying 11 percent of the nation's oil, a small percentage of tank cars are puncture-resistant, Udall said.