The Obama administration says the containment cap on the leaking Gulf of Mexico oil well is now capturing 15,000 barrels of crude a day.
Coast Guard Admiral Thad Allen, who leads the federal response to the spill, told reporters Wednesday that while the containment efforts continue to progress, he is not ready to declare victory.
Allen said officials are still trying to get accurate numbers on the amount of oil leaking from the well and that until then, they cannot accurately gauge the impact of the containment effort.
The admiral said additional vessels heading to the Gulf will increase the capacity to process oil as well as burn off natural gas and excess oil.
Meanwhile, Interior Secretary Ken Salazar pledged to a Senate panel Wednesday that the government will get to the root cause of the spill. He said the government and the American people will know what happened, and those responsible will be held accountable.
Salazar testified at one of five hearings the U.S. Congress is holding Wednesday to examine the massive seven-week-old oil spill.
The Senate is holding two hearings, while the House of Representatives has three oil spill-related hearings scheduled.
Admiral Allen also said the Coast Guard has sent a letter to oil company BP calling for the firm to begin a long-term containment plan that includes measures to ensure the capture of the oil will not be uninterrupted for any reason, including hurricanes.
The Coast Guard gave BP 72 hours from the receipt of the letter to comply.
Admiral Allen is meeting with BP Chief Executive Officer Tony Hayward Wednesday to discuss BP's response to claims filed by people and businesses affected by the spill. In a letter to Hayward Tuesday, Allen said the company has not responded to repeated requests for specific information showing how BP is responding.
In other developments, the White House says President Barack Obama is expected to return to the Gulf Coast next Monday and Tuesday, to inspect how the spilled oil is affecting the coastlines of the southern states of Mississippi, Alabama and Florida.
The damage was caused by an offshore oil rig explosion on April 20 that killed 11 people. The rig sank two days later.
Oil residue continues to spread to fragile Gulf coastlines, coating wildlife in a black ooze and threatening the ecology and livelihoods of the region.