NEW YORK/HOUSTON—Bakken crude prices are set to weaken from already low levels in coming months, with the frigid winter in North Dakota likely to disrupt rail loadings and worsen bottlenecks as production soars, traders and executives said.

U.S. oil producers ramped up production in the nation’s third-largest oil patch, boosting crude output to a record 1.3 million barrels per day (bbl/d) in October, overwhelming pipelines and rail cars.

The region’s pipeline capacity is just 1.25 million bbl/d, per market intelligence firm Genscape, forcing producers in North Dakota to rely on less-efficient rail, which could face difficulties operating in the winter. In addition, nearby Canadian producers also grappling with bottlenecks are pushing more oil into the United States, worsening the constraints.

Bakken crude traded at a record $20-per-barrel discount to U.S. crude futures last week, and last traded at a $13.50-per-barrel discount on Nov. 9.

Refinery maintenance exacerbated the discounts but as work wraps up, prices could find some support, company executives said.

Discounts on Bakken oil are nothing new, due to capacity constraints that forced refiners to rely on rail. The startup of Energy Transfer’s Dakota Access pipeline in 2017 changed that, but record production is straining capacity again.

“That basin is flush with barrels and there’s no way out,” Rick Hessling, senior vice president at U.S. refiner Marathon Petroleum Corp., said in an earnings call last week, adding that winter will make rail loadings more difficult. “We kind of see that as a perfect storm.”

Dakota Access pipeline was full in October, according to Genscape’s latest data, while one of the other major lines had an 85% utilization rate.

North Dakota’s crude production typically is not affected enough to lift prices the winter, but rail operations face severe challenges in the frigid weather, said John Zanner, crude analyst at RBN Energy.

“Winter weather makes crude-by-rail operations much more difficult. You have stuff freeze up, especially in North Dakota,” Zanner said.

Energy Transfer LP (NYSE: ET) plans to expand the Dakota Access pipeline system to as much as 570,000 bbl/d from about 525,000 bbl/d currently.

New pipeline and refining projects have been announced, but takeaway capacity will remain tight in the near-term as they get completed, analysts said. That is more apparent after a judge halted construction on the Keystone XL pipeline from Canada, potentially adding to a supply glut.

Several Canadian producers have already announced production cuts due to bottlenecks, but that is not enough. “We’re going to need curtailment and higher rail capacity,” one trader at a merchant said.