The U.S. government has until Thursday to respond to oil giant BP's accusation that it is withholding thousands of documents that could prove the size of the Deepwater Horizon oil spill in 2010 was smaller than originally reported. The size of the spill will play a crucial role as the courts determine the scope of BP's liability following the worst environmental disaster in U.S. history.

Last Thursday, embattled BP (NYSE: BP) accused the government of hiding critical data and reports that show that the oil spill wasn't as serious as prosecutors claim and requested the court to compel the government to release these documents. On Friday, U.S. Magistrate Sally Shushan in New Orleans gave U.S. prosecutors until Thursday to answer these assertions.

The government, one of many plaintiffs suing BP over the April 20 explosion of the Deepwater Horizon rig that killed 11 workers, says that 4.9 million barrels of oil were spilled in the aftermath of the accident. BP contends that number is overestimated.

Under the Clean Water Act, BP could pay anywhere from $1,100 per barrel to $4,300 per barrel if BP is found negligent in the Gulf spill. The higher amount would more likely be awarded if the government spill estimates are sustained.

BP already struck a $7.8 billion settlement with thousands of land and business owners, and could pay billions more if and when the case reenters court.

BP and prosecutors could still settle outside court. Both parties are expected to meet in the next few days to iron out disagreements regarding the disclosure of the documents, the AP said.

Wyn Hornbuckle, a spokesman for the Department of Justice, declined to comment citing pending litigation.

Request for comment from BP were unreturned by publication time.

Shares of BP rose 34 cents, or nearly 1 percent, to close at $45.34 on Monday.