According to the thirty-year-old law, in the US, diluted bitumen coming from the Alberta tar sands is not classified as oil. Pipeline operators planning to transport the corrosive substance across the US – with both old and new pipelines like the Keystone XL - are exempt from paying into the federal Oil Spill Liability Trust Fund.

Environmental impacts of the oil spill in central Arkansas began to come into focus as officials said a couple of dead ducks and 10 live oily birds were found after an ExxonMobil Corp. pipeline ruptured last week.

"I'm an animal lover, a wildlife lover, as probably most of the people here are," Faulkner County Judge Allen Dodson told reporters. "We don't like to see that. No one does." Dodson said emergency crews prevented the oil from entering waterways. The judge issued an emergency declaration following the spill and is involved in coordinating clean-up efforts among federal, state and local agencies and Exxon. The Exxon pipeline will not operate until the court says it can hold diluted bitumen again.