The National Resource Defense Council said in a 16-page report that conventional crude oil pipelines "appear to pose new and significant risks of pipeline leaks or ruptures due to corrosion" when they carry tar sands oil.
"There are many indications that diluted bitumen (tar sands oil) is significantly more corrosive to pipeline systems than conventional crude," the report reads.
The NRDC said most U.S. regulations are designed for conventional crude oil and don't address much in terms of oil sands.
"Without much public knowledge or a change in safety standards, U.S. pipelines are carrying increasing amounts of the corrosive raw form of tar sands oil," the NRDC finds.
The New York environmental group points to an increased frequency of spills through aging pipeline networks that it says can't handle tar sands oil.
Environmentalists are worried about the potential consequences of the planned Keystone XL pipeline that would carry tar sands oil to southern U.S. refineries, which the NRDC said are near sensitive land and aquifers.
Canada's Energy Resources Conservation Board said there was "no indication" that bitumen was more corrosive than conventional crude and denied the accuracy of much the NRDC's report.
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