Refineries along the Texas Gulf Coast began rapidly restarting following last week's winter storm that shut down the state's fuel processing and petrochemical industries with the lowest freezing temperatures in a generation.

The freeze knocked out power for millions of Texans and idled nearly a quarter of national refining capacity. The storm's effect on refining rivaled that of 2017's Hurricane Harvey, but also brought the added problems of freezing natural gas and water lines that will make it harder for facilities to restart safely.

The largest U.S. refinery, Motiva Enterprises 607,000 barrel-per-day Port Arthur plant, filed a notice with the Texas Commission on Environmental Quality (TCEQ) of plans to begin a 17-day restart on Monday.

Sources familiar with operations said the refinery must repair water pipes throughout the plant that froze and cracked when temperatures dropped well below freezing a week ago.

Marathon Petroleum Corp's 585,000-bpd Galveston Bay Refinery in Texas City, Texas, restarted the co-generation unit, which produces power and steam, said sources familiar with plant operations. Process lines, fittings and water pipes throughout the refinery need repair, the sources said.

Exxon Mobil Corp began an attempt on Monday at its 560,500-bpd Baytown, Texas, refinery. External power was restored to the plant over the weekend, said sources familiar with plant operations.

Exxon's 369,024-bpd Beaumont refinery also began restarting on Sunday, the company said.

Two refineries were restarting in Corpus Christi, Texas, and a third was making preparations to start-up again.

Valero's 290,000-bpd plant began restarting on Saturday and Flint Hills Resources 338,500-bpd began restart on Sunday, according to filings with the TCEQ.

Citgo said it was preparing to restart its 167,500-bpd Corpus Christi refinery.

Valero is also restarting its 335,000-bpd Port Arthur refinery. The company also restarted the crude distillation unit at its 125,000-bpd Meraux, Louisiana, refinery.