The United States could be at greater risk than ever of a major pipeline spill, according to a report released Thursday by several environmental groups.

The reason why? A fast-growing dependence on Alberta’s oil sands.

Albertan officials, meanwhile, called the report’s assumptions “flawed”, “misleading” and “incorrect”.

Oil sands energy comes in the form of bitumen, a viscous substance that won’t flow through pipelines unless it’s mixed with condensate.

The resulting “dilbit” is “highly corrosive, acidic and potentially unstable,” argues Thursday’s report.

Its authors – the Natural Resources Defense Council, Pipeline Safety Trust, National Wildlife Federation and Sierra Club – believe transporting dilbit is more dangerous than conventional fossil fuels.

The Alberta pipeline system, which carries more dilbit than the American system, experienced 16 times more spills between 2002 and 2010, according to the report’s analysis.

The United States has historically imported synthetic crude from Alberta's oil sands – basically bitumen that’s been refined to a point where it resembles conventional oil.

But as production increases, more and more dilbit is being pumped to U.S. refineries. In fact, as the report notes, dilbit imports have grown “almost fivefold” over the past ten years.

“By its nature,” wrote the NRDC’s Susan Casey-Lefkowitz on her blog, “raw tar sands oil or diluted bitumen is more corrosive and more likely to result in pipeline failures.”

Alberta’s Energy Resources Conservation Board was quick to issue a response Thursday morning, claiming the report “contains misleading statements on pipeline safety in Alberta and on the characteristics of diluted bitumen.”

The ERCB, which regulates Alberta’s energy sector, questioned the report’s methodology and noted that it wasn’t contacted by any of the authors.

Geoff Dembicki reports for the Tyee.