A deep freeze across Texas took a toll on the energy industry in the largest U.S. crude-producing state, shutting oil refineries and forcing restrictions from natural gas pipeline operators.

The cold snap prompted the state’s electric grid operator to impose rotating blackouts, while President Joe Biden declared an emergency on Monday, unlocking federal assistance to Texas according to news source Reuters.

Texas produces roughly 4.6 million barrels of oil a day and is home to some of the nation’s largest refineries, spread throughout the Gulf Coast. In Midland, heart of the U.S. Permian shale region, temperatures were in the single digits Fahrenheit.

Motiva Enterprises said it was shutting down its Port Arthur, Texas, complex, which includes its 607,000 bpe refinery, the largest in the United States.

Exxon also began shutting its 369,024 bpd Beaumont, Texas, refinery, while its Baton Rouge facility in Louisiana experienced operational issues.

Citgo Petroleum Corp said some units at its 167,500 bpd Corpus Christi, Texas, refinery were being shut.

Sources familiar with plant operations said earlier that the crude distillation unit, a reformer and a hydrotreater were shut by cold weather at the refinery, with all other units also being powered down.

The cold snap also forced Lyondell Basell’s 263,776-bpd Houston refinery to operate at minimum production and shut most units at Marathon’s 585,000 bpd Galveston Bay plant.

“We are also getting reports of power outages across the Permian, which are expected to continue over the weekend if the current weather system persists. This may result in intermittent production shut-ins, with a moderate impact on Permian oil production expected in February,” Rystad Energy’s head of oil markets, Bjornar Tonhaugen said, in a note.

Energy distribution was stalled across large parts of the United States.

Kinder Morgan’s Natural Gas Pipeline Co. reported capacity constraints at various locations on its pipeline system, while Enable Gas Transmission said it was taking measures to ensure adequate supply for customers.

Oil pipeline operator Enbridge on Monday said a 585,000-bpd crude oil pipeline that runs from its terminal near Pontiac, Illinois, outside of Chicago, to the largest U.S. oil storage hub in Cushing, Oklahoma, was halted because of power outages. “Crews are working with electric utility providers to restore power to Line 59,” as the pipeline is called, said Enbridge spokesman Michael Barnes. “The power failure is due to the winter storm the U.S. is experiencing.”