Canadian heavy crude’s discount to U.S. benchmark oil hit the widest since Alberta introduced a plan to limit the province’s production more than a year ago, threatening more adversity for the beleaguered industry.

Western Canadian Select’s discount to West Texas Intermediate reached US$24.05 a barrel on Friday, the biggest gap since Nov. 30, 2018, the last trading day before Alberta announced that it would order producers to cut about 8.7% of the province’s daily production to help clear a glut of crude that had hammered prices.

The recent price decline heightens the troubles of an oil-sands industry that holds the world’s third-largest reserves but lacks the capacity to ship all of its production to refineries in the U.S. Midwest and Gulf Coast. With three key pipeline projects stalled, producers are increasingly relying on more costly rail shipments at a time when storage tanks throughout Alberta are close to full.

The widening differentials suggest that Canadian oil is at high risk of a “blowout,” Credit Suisse analyst Manav Gupta said in a report this week. If the differential widens beyond US$25 a barrel, the “Alberta government might be forced to step back in and raise the volumes on mandated cuts to control bloating inventory situation,” he said.

Alberta has progressively increased the province’s allowed production since the limits went into effect at the start of last year. The output targets for this month and next are set at 3.81 million barrels a day, only about 75,000 barrels less than before the program was implemented. The rising production has caused increased rationing on Enbridge Inc.’s heavy oil line, and inventories already had built to record highs at the end of November after a rail strike and a temporary outage on TC Energy Corp.’s Keystone pipeline.

Western Canada is seeing some improvements on the pipeline front, with about 100,000 barrels of daily shipping capacity added on Enbridge’s Mainline late last year and an additional 50,000 barrels being added to Keystone early this year, said Kavi Bal, a spokesman for Alberta’s Ministry of Energy.

“We will continue to closely monitor the situation ensuring that Albertans receive the best value for their resources,” Bal said in an email.