BP PLC accuses the federal government of improperly withholding scientific documents that could show it overestimated the amount of oil that spewed into the Gulf of Mexico from the company's Macondo well.

Late Thursday, the oil company asked U.S. Magistrate Sally Shushan in New Orleans to order the government to turn over thousands of documents that appear to relate to "flow rate issues" and the work of scientists who served on the government's "Flow Rate Technical Group" following the 2010 spill.

On Friday, Shushan gave the government until April 5 to reply to BP's argument. She also ordered the parties to meet and try to reach an agreement on sharing documents.

The government estimates 4.9 million barrels of oil spewed from the well off the coast of Louisiana, but the company says the technical group's earlier estimates may have been lower. BP faces penalties based on how much oil spilled.

BP argues the government can't withhold more than 10,000 documents on flow-rate issues because they concern factual issues, not policy determinations. The government can't invoke the "deliberative process" privilege to protect those documents, the company argues.

A Justice Department spokesman said he couldn't comment because it involves pending litigation.

BP said the government's 4.9 million barrel estimate, announced on Aug. 2, 2010, was the fourth official estimate released by the technical group. Its earlier estimates "suggested a lower measured flow rate," the company said.

"The challenged documents are central to this case, and this factor also weighs heavily in favor of disclosure," BP attorneys wrote in Thursday's court filing. "All documents that reflect data underlying, debates over, criticism of, errors in, or otherwise elucidate flow rate facts and estimates are highly relevant to BP's defense of this litigation."

On March 2, BP announced a multibillion dollar settlement with plaintiffs' attorneys representing more than 100,000 individuals and businesses who blame the spill for economic losses. But the deal doesn't resolve the Justice Department's claims against the company over the blowout, which triggered a deadly explosion on the Deepwater Horizon rig and spawned the nation's worst offshore oil spill.

BP says the government is improperly withholding many emails between members of the technical group.

"The (technical group) had no agency policymaking authority _ it was a group of non-government scientists charged with a factual determination concerning quantification of flow during the spill," company lawyers wrote. "There is therefore no basis for the United States' claim that communications that include (technical group) members reflect internal policymaking."