Not just any oil spill. The Keystone pipeline dumped notoriously hard-to-clean 'dilbit' in Kansas...

The spill in Kansas is now the second-largest spill of tar sands crude on U.S. soil. And scientists say this stuff comes with major complications for containing and cleaning it.
Each day that passes, the hundreds of thousands of gallons of sludgy oil coating Mill Creek in north-central Kansas become harder to clean up.

That’s because the pipeline that busted just outside the town of Washington on Dec. 7 doesn’t carry conventional crude oil. It carries a product of the Canadian tar sands called diluted bitumen that changes dramatically in chemical composition and behavior soon after escaping from pipes.

A National Academies of Sciences study found that transformation means the crude oil can start sinking below the water’s surface in a matter of days.

The Kansas spill occurred eight days ago and is now the second-largest spill of tar sands crude on U.S. soil.