Three days after an Exxon pipeline in Central Arkansas burst and soaked the town of Mayflower in thousands of barrels of crude oil, the cleanup is ongoing. At last count, 12,000 barrels of tar sands oil and water have been dumped on the small town.

“Tar sands oil has the highest carbon content of any oil that we know of,” said 350.org executive director May Boeve on the April 1 edition of msnbc’s All In with Chris Hayes. “And right now, the spill we’re seeing in Arkansas is a devastating problem. And the real shocker about it … is that this pipeline carries one tenth of what the proposed Keystone XL pipeline would carry.”

One Mayflower local recorded a video of the spill:

The incident comes at an awkward time for those in favor of extending the Keystone Pipeline to bring crude oil through the United States. Referring to “the mess in Arkansas,” Rep. Ed Markey (D-Mass.), an opponent of the Keystone XL project, said “Americans are realizing that transporting large amounts of this corrosive and polluting fuel is a bad deal for American taxpayers and for our environment.”

The Mayflower spill underscores how little is known about the risks of crude oil transportation, even as America ramps up its oil production.