TransCanada Corp has asked the U.S. government to suspend its review of the $8 billion Keystone XL pipeline project that would bring heavy oil from Alberta to U.S. refineries.
If granted by the U.S. State Department, the delay would almost certainly hand the decision for the long-delayed project to a future president rather than Barack Obama, a Democrat.
Below are key facts and issues surrounding the project that has drawn opposition from environmental groups.
The 1,179-mile (1,900-km) Keystone XL pipeline would move 830,000 barrels per day of oil sands crude from Hardisty, Alberta, across the U.S. border to Steele City, Nebraska, where it would connect with a previously approved line.
The $8 billion project is backed by TransCanada, Canada's No. 2 pipeline company, but requires a Presidential Certificate from the Obama administration to allow the line to cross the border.
TransCanada first applied for that needed U.S. approval for the Keystone XL in 2008.
Refiners on the Gulf Coast want the line to supply the heavy oil they need and supplant uncertain supplies from Mexico and Venezuela. Canadian oil sands producers want to tap the world's largest refining market for their oil and boost the price they get for their crude.
Environmentalists have made pipelines, and Keystone XL in particular, the proxy for their battle against exploiting Alberta's oil sands, where, they say, production techniques emit massive amounts of carbon dioxide, one of the greenhouse gases blamed for global warming.
Republican leaders have said approving the long-delayed project was a top priority when they gained control of the Senate.
The U.S. State Department has yet to grant approval for the pipeline and many industry analysts expect President Barack Obama to veto the project, after he questioned how beneficial it will be for the United States.
Obama has said he was skeptical of TransCanada's claims about the number of jobs the project would create and said he was concerned that oil extraction from Canada's oil sands was "extraordinarily dirty".
In September, Democratic U.S. presidential candidate Hillary Clinton broke her silence on the issue and said she opposed it.
Most Republican candidates have said they want the pipeline built.
THE COURT CASE:
Opposition in Nebraska has been one of several major hurdles facing the Keystone XL project.
The line's route through Nebraska has been the subject of a court case in the state over whether former Governor Dave Heineman was entitled to approve the route.
A Nebraska Supreme Court decision in January this year ruled in support of the pipeline, but a number of Nebraskan landowners filed suits against TransCanada alleging the project violated the state's constitution.
In September, Transcanada changed tack and applied for approval through the Nebraska Public Service Commission.
(Reporting by Josephine Mason; Additional reporting by Valerie Volcovici in Washington; Editing by Lisa Shumaker)