TransCanada Corp’s existing Keystone pipeline has leaked substantially more oil and more often, in the United States than indicated in risk assessments the company provided to regulators before the project began operating in 2010, according to documents reviewed by Reuters.

The Canadian company is now seeking to expand the pipeline system linking Alberta’s oil fields to US refineries with its proposed Keystone XL project, which has President Donald Trump‘s backing.

The existing 2,147-mile Keystone system from Hardisty, Alberta, to the Texas coast has had three significant leaks in the United States since it began operating in 2010, including a 5,000-barrel spill this month in rural South Dakota and two others, each about 400 barrels, in South Dakota in 2016 and North Dakota in 2011.

Before constructing the pipeline, TransCanada provided a spill risk assessment to regulators that estimated the chance of a leak of more than 50 barrels to be “not more than once every seven to 11 years over the entire length of the pipeline in the United States,” according to its South Dakota operating permit.

For South Dakota alone, where the line has leaked twice, the estimate was for a “spill no more than once every 41 years.”

The spill risk analysis was conducted by global risk management company DNV GL. A spokesman for DNV did not respond to a request for comment.

Members of South Dakota’s Public Utilities Commission told Reuters last week they could revoke TransCanada’s operating permit if an initial probe of last week’s spill shows it violated the terms of the license.

Those terms include requirements for standards for construction, regular inspections of pipeline infrastructure, and other environmental safeguards.

“They testified that this is going to be a state-of-the-art pipeline,” said one of the commissioners, Gary Hanson. “We want to know the pipeline is going to operate in a fashion that is safe and reliable. So far it’s not going well.”

TransCanada shut a section of the line while it cleans up the leak, which occurred near the town of Aberdeen on 16 November. An official did not respond to a request for comment.

Sioux from Standing Rock claim victory over Dakota Pipeline Show all 21 1 /21 Sioux from Standing Rock claim victory over Dakota Pipeline Sioux from Standing Rock claim victory over Dakota Pipeline CANNON BALL, ND - DECEMBER 05: Despite blizzard conditions, military veterans march in support of the "water protectors" at Oceti Sakowin Camp on the edge of the Standing Rock Sioux Reservation on December 5, 2016 outside Cannon Ball, North Dakota. Over the weekend a large group of military veterans joined native Americans and activists from around the country who have been at the camp for several months trying to halt the construction of the Dakota Access Pipeline. Yesterday the US Army Corps of Engineers announced that it will not grant an easement for the pipeline to cross under a lake on the Sioux Tribes Standing Rock reservation. The proposed 1,172-mile-long pipeline would transport oil from the North Dakota Bakken region through South Dakota, Iowa and into Illinois. (Photo by Scott Olson/Getty Images) Getty Images Sioux from Standing Rock claim victory over Dakota Pipeline CANNON BALL, ND - DECEMBER 04: Fireworks fill the night sky above Oceti Sakowin Camp as activists celebrate after learning an easement had been denied for the Dakota Access Pipeline near the edge of the Standing Rock Sioux Reservation on December 4, 2016 outside Cannon Ball, North Dakota. The US Army Corps of Engineers announced today that it will not grant an easement to the Dakota Access Pipeline to cross under a lake on the Sioux Tribes Standing Rock reservation, ending a months-long standoff. (Photo by Scott Olson/Getty Images) Getty Images Sioux from Standing Rock claim victory over Dakota Pipeline CANNON BALL, ND - DECEMBER 05: Despite blizzard conditions, military veterans march in support of the "water protectors" at Oceti Sakowin Camp on the edge of the Standing Rock Sioux Reservation on December 5, 2016 outside Cannon Ball, North Dakota. Over the weekend a large group of military veterans joined native Americans and activists from around the country who have been at the camp for several months trying to halt the construction of the Dakota Access Pipeline. Yesterday the US Army Corps of Engineers announced that it will not grant an easement for the pipeline to cross under a lake on the Sioux Tribes Standing Rock reservation. The proposed 1,172-mile-long pipeline would transport oil from the North Dakota Bakken region through South Dakota, Iowa and into Illinois. (Photo by Scott Olson/Getty Images) Getty Images Sioux from Standing Rock claim victory over Dakota Pipeline CANNON BALL, ND - DECEMBER 04: Fireworks fill the night sky above Oceti Sakowin Camp as activists celebrate after learning an easement had been denied for the Dakota Access Pipeline near the edge of the Standing Rock Sioux Reservation on December 4, 2016 outside Cannon Ball, North Dakota. The US Army Corps of Engineers announced today that it will not grant an easement to the Dakota Access Pipeline to cross under a lake on the Sioux Tribes Standing Rock reservation, ending a months-long standoff. (Photo by Scott Olson/Getty Images) Getty Images Sioux from Standing Rock claim victory over Dakota Pipeline CANNON BALL, ND - DECEMBER 05: Despite blizzard conditions, military veterans march in support of the "water protectors" at Oceti Sakowin Camp on the edge of the Standing Rock Sioux Reservation on December 5, 2016 outside Cannon Ball, North Dakota. Over the weekend a large group of military veterans joined native Americans and activists from around the country who have been at the camp for several months trying to halt the construction of the Dakota Access Pipeline. Yesterday the US Army Corps of Engineers announced that it will not grant an easement for the pipeline to cross under a lake on the Sioux Tribes Standing Rock reservation. The proposed 1,172-mile-long pipeline would transport oil from the North Dakota Bakken region through South Dakota, Iowa and into Illinois. (Photo by Scott Olson/Getty Images) Getty Images Sioux from Standing Rock claim victory over Dakota Pipeline CANNON BALL, ND - DECEMBER 04: Native American and other activists celebrate after learning an easement had been denied for the Dakota Access Pipeline at Oceti Sakowin Camp on the edge of the Standing Rock Sioux Reservation on December 4, 2016 outside Cannon Ball, North Dakota. The US Army Corps of Engineers announced today that it will not grant an easement to the Dakota Access Pipeline to cross under a lake on the Sioux Tribes Standing Rock reservation, ending a months-long standoff. (Photo by Scott Olson/Getty Images) Getty Sioux from Standing Rock claim victory over Dakota Pipeline CANNON BALL, ND - DECEMBER 04: Chief Arvol Looking Horse of the Lakota/Dakota/Nakota Nation listens to speakers during an interfaith ceremony at Oceti Sakowin Camp on the edge of the Standing Rock Sioux Reservation on December 4, 2016 outside Cannon Ball, North Dakota. Native Americans and activists from around the country have been gathering at the camp for several months trying to halt the construction of the Dakota Access Pipeline. Today the US Army Corps of Engineers announced that it will not grant an easement for the pipeline to cross under a lake on the Sioux Tribes Standing Rock reservation, ending the months-long standoff. The proposed 1,172-mile-long pipeline would transport oil from the North Dakota Bakken region through South Dakota, Iowa and into Illinois. (Photo by Scott Olson/Getty Images) Getty Images Sioux from Standing Rock claim victory over Dakota Pipeline CANNON BALL, ND - DECEMBER 04: An Native American activist rides down fom a ridge which overlooks Oceti Sakowin Camp on the edge of the Standing Rock Sioux Reservation on December 4, 2016 outside Cannon Ball, North Dakota. Native Americans and activists from around the country have been gathering at the camp for several months trying to halt the construction of the Dakota Access Pipeline. The proposed 1,172-mile-long pipeline would transport oil from the North Dakota Bakken region through South Dakota, Iowa and into Illinois. (Photo by Scott Olson/Getty Images) Getty Images Sioux from Standing Rock claim victory over Dakota Pipeline CANNON BALL, ND - DECEMBER 05: Despite blizzard conditions, military veterans march in support of the "water protectors" at Oceti Sakowin Camp on the edge of the Standing Rock Sioux Reservation on December 5, 2016 outside Cannon Ball, North Dakota. Over the weekend a large group of military veterans joined native Americans and activists from around the country who have been at the camp for several months trying to halt the construction of the Dakota Access Pipeline. Yesterday the US Army Corps of Engineers announced that it will not grant an easement for the pipeline to cross under a lake on the Sioux Tribes Standing Rock reservation. The proposed 1,172-mile-long pipeline would transport oil from the North Dakota Bakken region through South Dakota, Iowa and into Illinois. (Photo by Scott Olson/Getty Images) Getty Images Sioux from Standing Rock claim victory over Dakota Pipeline CANNON BALL, ND - DECEMBER 04: Political activist Cornel West listen to speakers during an interfaith ceremony at Oceti Sakowin Camp on the edge of the Standing Rock Sioux Reservation on December 4, 2016 outside Cannon Ball, North Dakota. Native Americans and activists from around the country have been gathering at the camp for several months trying to halt the construction of the Dakota Access Pipeline. Today the US Army Corps of Engineers announced that it will not grant an easement for the pipeline to cross under a lake on the Sioux Tribes Standing Rock reservation, ending the months-long standoff. The proposed 1,172-mile-long pipeline would transport oil from the North Dakota Bakken region through South Dakota, Iowa and into Illinois. (Photo by Scott Olson/Getty Images) Getty Images Sioux from Standing Rock claim victory over Dakota Pipeline Activists hold hands during a prayer circle as they try to surround the entire camp at Oceti Sakowin Camp on the edge of the Standing Rock Sioux Reservation on December 4, 2016 outside Cannon Ball, North Dakota. Native Americans and activists from around the country gather at the camp trying to halt the construction of the Dakota Access Pipeline. / AFP / JIM WATSON (Photo credit should read JIM WATSON/AFP/Getty Images) AFP/Getty Images Sioux from Standing Rock claim victory over Dakota Pipeline Activists celebrate at Oceti Sakowin Camp on the edge of the Standing Rock Sioux Reservation on December 4, 2016 outside Cannon Ball, North Dakota, after hearing that the Army Corps of Engineers has denied the current route for the Dakota Access pipeline. / AFP / JIM WATSON (Photo credit should read JIM WATSON/AFP/Getty Images) AFP/Getty Images Sioux from Standing Rock claim victory over Dakota Pipeline CANNON BALL, ND - DECEMBER 04: Chief Arvol Looking Horse (L) of the Lakota/Dakota/Nakota Nation listens as political activist Cornel West speaks during an interfaith ceremony at Oceti Sakowin Camp on the edge of the Standing Rock Sioux Reservation on December 4, 2016 outside Cannon Ball, North Dakota. Native Americans and activists from around the country have been gathering at the camp for several months trying to halt the construction of the Dakota Access Pipeline. Today the US Army Corps of Engineers announced that it will not grant an easement for the pipeline to cross under a lake on the Sioux Tribes Standing Rock reservation, ending the months-long standoff. The proposed 1,172-mile-long pipeline would transport oil from the North Dakota Bakken region through South Dakota, Iowa and into Illinois. (Photo by Scott Olson/Getty Images) Getty Images Sioux from Standing Rock claim victory over Dakota Pipeline CANNON BALL, ND - DECEMBER 05: Military veterans from Southern California collect firewood for their campsite at Oceti Sakowin Camp on the edge of the Standing Rock Sioux Reservation on December 5, 2016 outside Cannon Ball, North Dakota. Over the weekend a large group of military veterans joined native Americans and activists from around the country who have been at the camp for several months trying to halt the construction of the Dakota Access Pipeline. Yesterday the US Army Corps of Engineers announced that it will not grant an easement for the pipeline to cross under a lake on the Sioux Tribes Standing Rock reservation. The proposed 1,172-mile-long pipeline would transport oil from the North Dakota Bakken region through South Dakota, Iowa and into Illinois. (Photo by Scott Olson/Getty Images) Getty Images Sioux from Standing Rock claim victory over Dakota Pipeline CANNON BALL, ND - DECEMBER 05: Despite blizzard conditions, military veterans march in support of the "water protectors" at Oceti Sakowin Camp on the edge of the Standing Rock Sioux Reservation on December 5, 2016 outside Cannon Ball, North Dakota. Over the weekend a large group of military veterans joined native Americans and activists from around the country who have been at the camp for several months trying to halt the construction of the Dakota Access Pipeline. Yesterday the US Army Corps of Engineers announced that it will not grant an easement for the pipeline to cross under a lake on the Sioux Tribes Standing Rock reservation. The proposed 1,172-mile-long pipeline would transport oil from the North Dakota Bakken region through South Dakota, Iowa and into Illinois. (Photo by Scott Olson/Getty Images) Getty Images Sioux from Standing Rock claim victory over Dakota Pipeline CANNON BALL, ND - DECEMBER 03: Activists participate in an art project conceived by Cannupa Hunska Luger, from the Standing Rock Sioux Tribe, at Oceti Sakowin Camp on the edge of the Standing Rock Sioux Reservation on December 3, 2016 outside Cannon Ball, North Dakota. Native Americans and activists from around the country have been gathering at the camp for several months trying to halt the construction of the Dakota Access Pipeline. The proposed 1,172-mile-long pipeline would transport oil from the North Dakota Bakken region through South Dakota, Iowa and into Illinois. (Photo by Scott Olson/Getty Images) Getty Images Sioux from Standing Rock claim victory over Dakota Pipeline CANNON BALL, ND - DECEMBER 05: Military veterans are briefed on cold-weather safety issues and their overall role at Oceti Sakowin Camp on the edge of the Standing Rock Sioux Reservation on December 5, 2016 outside Cannon Ball, North Dakota. Over the weekend a large group of military veterans joined native Americans and activists from around the country who have been at the camp for several months trying to halt the construction of the Dakota Access Pipeline. Yesterday the US Army Corps of Engineers announced that it will not grant an easement for the pipeline to cross under a lake on the Sioux Tribes Standing Rock reservation. The proposed 1,172-mile-long pipeline would transport oil from the North Dakota Bakken region through South Dakota, Iowa and into Illinois. (Photo by Scott Olson/Getty Images) Getty Images Sioux from Standing Rock claim victory over Dakota Pipeline CANNON BALL, ND - DECEMBER 04: Native American and other activists celebrate after learning an easement had been denied for the Dakota Access Pipeline at Oceti Sakowin Camp on the edge of the Standing Rock Sioux Reservation on December 4, 2016 outside Cannon Ball, North Dakota. The US Army Corps of Engineers announced today that it will not grant an easement to the Dakota Access Pipeline to cross under a lake on the Sioux Tribes Standing Rock reservation, ending a months-long standoff. (Photo by Scott Olson/Getty Images) Getty Images Sioux from Standing Rock claim victory over Dakota Pipeline CANNON BALL, ND - DECEMBER 04: Native American activists celebrate after learning an easement had been denied for the Dakota Access Pipeline at Oceti Sakowin Camp on the edge of the Standing Rock Sioux Reservation on December 4, 2016 outside Cannon Ball, North Dakota. The US Army Corps of Engineers announced today that it will not grant an easement to the Dakota Access Pipeline to cross under a lake on the Sioux Tribes Standing Rock reservation, ending a months-long standoff. (Photo by Scott Olson/Getty Images) Getty Images Sioux from Standing Rock claim victory over Dakota Pipeline CANNON BALL, ND - DECEMBER 04: Native American and other activists celebrate after learning an easement had been denied for the Dakota Access Pipeline at Oceti Sakowin Camp on the edge of the Standing Rock Sioux Reservation on December 4, 2016 outside Cannon Ball, North Dakota. The US Army Corps of Engineers announced today that it will not grant an easement to the Dakota Access Pipeline to cross under a lake on the Sioux Tribes Standing Rock reservation, ending a months-long standoff. (Photo by Scott Olson/Getty Images) Getty Images Sioux from Standing Rock claim victory over Dakota Pipeline Activists celebrate at Oceti Sakowin Camp on the edge of the Standing Rock Sioux Reservation on December 4, 2016 outside Cannon Ball, North Dakota, after hearing that the Army Corps of Engineers has denied the current route for the Dakota Access pipeline. The US Army Corps of Engineers on Sunday announced they will no longer allow the Dakota Access Pipeline to cross under a lake on the Standing Rock reservation in North Dakota, marking a huge win for Native Americans and protesters who had long opposed the construction. / AFP / JIM WATSON (Photo credit should read JIM WATSON/AFP/Getty Images) AFP/Getty Images

The spill took place days before regulators in neighbouring Nebraska approved a route for TransCanada’s proposed Keystone XL pipeline through the state, lifting the last major regulatory hurdle for the expansion that has been delayed for years by environmental opposition.

Mr Trump handed TransCanada a presidential permit for Keystone XL in March, reversing former President Barack Obama‘s decision to reject the line on economic and environmental grounds, saying that it would create jobs and boost national security.

TransCanada’s spill analysis for Keystone XL, which would cross Montana, South Dakota and Nebraska, estimates 2.2 leaks per decade with half of those at volumes of 3 barrels or less. It estimated that spills exceeding 1,000 barrels would occur at a rate of once per century.