The nation's largest oil refinery at Port Arthur in Texas is in the final stages of being restarted, but it will still take until the weekend before it returns to anything close to business as usual, according to Motiva, which owns the plant.

"We expect the refinery to initially return to approximately 40 percent production by the end of this weekend, provided that the final assessments meet our operational standards," a statement from Motiva said on Tuesday.

The Saudi Arabia-owned refinery prides itself on being able to process 600,000 barrels of crude oil into nearly 300,000 barrels of gasoline and other refined products each day. But the record-breaking floods that accompanied Hurricane Harvey proved too much for the large facility, which was forced to close down on Aug. 30.

"We continue to work closely with state, local and federal governmental officials as well as disaster relief organizations to address storm impacts on our business and to aid our communities in their recovery," the company said. "Our highest priority remains the safety of our employees and community."

Other refineries were also marking progress. Valero, the largest independent refinery company in the world, said two of its refineries at Corpus Christi and Texas City are already operating at pre-hurricane rates.

Valero's Three Rivers refinery continues to ramp-up operations and its Houston facility will increase production rates as transportation and logistics infrastructure continues to recover from flooding. Valero's Port Arthur refinery "is in final stages of refinery assessment and making preparations to resume operations," a company update said.