Backyard NightmareCrude oil flowed down driveways and swamped grass lawns in Mayflower, Arkansas, after an oil pipeline ruptured Friday afternoon. At least 12,000 barrels of Canadian crude oil and water spilled into a housing development over the weekend, causing the evacuation of 22 homes in the Little Rock suburb. Here, spilled crude fills a drainage ditch near the evacuated homes.ExxonMobil's Pegasus pipeline, which is more than six decades old, runs from Patoka, Illinois, to Nederland, Texas, and can transport up to 90,000 barrels of oil per day. The company said Monday it was still investigating the cause of the spill, which the U.S. Environmental Protection Agency classified as "major." Cleanup is ongoing.

The Mayflower spill was the second in one week that involved tar sands crude. Last Wednesday, a train derailed in western Minnesota and leaked an estimated 350 barrels of oil. The transport of oil by rail in the United States has grown in recent years, as producers struggle to move new bounties of crude from Canada and North Dakota south to refineries. (See related story: "Oil Train Revival: North Dakota Relies on Rail to Deliver Its Crude.")

—Christina Nunez

Photograph by Jacob Slaton, Reuters

Pictures: Arkansas Oil Spill Darkens Backyards, Driveways

The pipeline rupture forces an evacuation of homes in Arkansas and highlights questions about safety in the push to move tar sands oil from Canada south to U.S. refineries.

Published April 3, 2013