In a statement, the company said it “believes this step is necessary to protect the interests of its employees, its shareholders and the company.” Transocean also said it wanted to consolidate all the lawsuits it is facing in one court, and establish a single fund from which “legitimate claims may be paid.”

Image Senators Frank R. Lautenberg, left, and Robert Menendez, Democrats of New Jersey, proposed Thursday to raise the liability limit in oil spills to $10 billion from $75 million. Credit... Mark Wilson/Getty Images

Also on Thursday, Ken Salazar, the Interior secretary, took a step toward a planned reorganization of the troubled Minerals Management Service, the agency responsible for regulating the safety and environmental practices of offshore oil drillers, as well as promoting oil exploration and collecting royalties from it.

Mr. Salazar, who announced earlier in the week that he intended to separate the agency’s two functions, named two senior department officials to begin planning for the breakup of the minerals agency and creation of its successors. He said the goal of the reorganization was to strengthen safety and environmental enforcement and to end the sometimes-too-close relationship between government officials and regulated companies.

“We have a responsibility to ensure that the operation and oversight of offshore operations are following the law, protecting the workers and guarding against future incidents and spills,” Mr. Salazar said in a letter to Congressional leaders seeking their opinions on the proposed overhaul.

BP, which has assumed responsibility for the bulk of claims arising from the spill, announced that the cost of responding to the disaster so far had amounted to an estimated $450 million, about $100 million more than the estimate earlier in the week.

The company said in a filing to the federal Securities and Exchange Commission that the tab included money it had given to Gulf Coast states and the federal government for their responses. The costs also include efforts to contain the spilling crude oil, continuing work to drill a relief well and settlements. So far 6,700 claims have been filed, of which about 1,000 have already been paid, according to the company statement.

In the gulf, efforts continued to stop the oil flowing from the damaged well, as BP said it was moving forward with several strategies to try to contain the spill, including inserting a tube into the broken drilling pipe to draw the oil out.