BP Managing Director Robert Dudley said a complex "top kill" operation started on Wednesday to try to halt the seabed well's flow by pumping heavy drilling fluids into it was "moving the way we want it to." But he told NBC's "Today Show" it was too early to say whether it had been successful.
The joint command center tackling the spill could not confirm or deny a Los Angeles Times report that the effort had succeeded, a spokeswoman said on Thursday.
"At the moment, we can't confirm or deny anything," she told Reuters, when asked about the Latimes.com report which cited Coast Guard Admiral Thad Allen. BP shares rose more than five percent in London trading.
As public anger and frustration rises over the spill, which is shaping up to be the worst in US history, Obama prepared to announce on Thursday a six-month extension of the moratorium on permits for new deepwater oil drilling while a commission investigates the Gulf spill.
Obama has come under increasing pressure from lawmakers and residents of the oil-stained coast to take over the disaster response if BP's latest tactic to plug the spewing oil fails.
Dudley told NBC the top kill effort was "as difficult as we expected and we'll know more later today and tomorrow."
"What you have is this titanic arm-wrestling match between two flows essentially going at each other," Dudley told CNN in one of several appearances on US TV networks.
The spill was triggered by a deadly April 20 blast aboard the Deepwater Horizon rig, which was leased by BP.
Dudley said BP had a "Plan B" if the top kill operation did not stanch the leaking well. "All along the seabed, out and around the well, we placed equipment to be ready to put in place very, very quickly with a second containment dome over the top of the well," he told CBS.
If the heavy fluids being pumped into the ruptured well halt its flow, cement will be injected in to seal it.
The company has lost more than a quarter of its market value since the explosion.
ECOLOGICAL DAMAGE, HEALTH WORRIES
Obama, who has described the Gulf crisis as "heartbreaking," is to outline his response to the oil spill at a 12:45 p.m. EDT/1645 GMT White House news conference.
The extended moratorium is a further setback for offshore drilling expansion, a key plank of Obama's energy overhaul, currently languishing in the US Senate. Democrats hoped the drilling component would attract Republican support for the bill, which also ramps up domestic production of renewable fuel sources and sets limits on greenhouse gas emissions.
"With the increased risks, the increased costs, it gives you a sense of where we're going," Obama said on a trip to California on Wednesday. "We're not going to be able to sustain this kind of fossil fuel use."
Alaska Senator Mark Begich said he had been told by the Interior Department that the administration's moratorium will include suspending applications for exploratory drilling in the Arctic until 2011.
As one of the country's worst environmental catastrophes unfolds on his watch, Obama is under increasing pressure from lawmakers and residents of the fouled coast to take over the disaster response if the top kill fails.
At risk is a unique ecosystem already battered by Hurricane Katrina, a lucrative seafood industry now largely shut down and the credibility of a first-term president's crisis management.
Worries about health risks from the crude spill were also increasing. The oil spill response command on Wednesday recalled 125 private commercial vessels that were helping with the containment operation in Breton Sound, Louisiana after four ship crewmembers reported health problems. They reported experiencing nausea, dizziness, headaches and chest pains.
The New York Times reported BP had tried to save money by taking a chance on the type of casing cement used on the well. The newspaper, which cited a BP document it received from a congressional investigator, said gases were leaking through the casing hours before the explosion.
BP CEO Tony Hayward says "a series of failures" led to the accident, but he has denied this had to do with cost saving.
PRAYING FOR SUCCESS
A top kill has never been done at the depths of the gushing well, one mile (1.6 km) down in the Gulf.
"I'm praying to God that it will work," said Troy Wetzel, 45, who owns a charter boat for sport fishermen in Venice, a fishing mecca in southern Louisiana recoiling from the impact of the spill.
In a sign that BP and the government were aligning after weeks of tension between the two camps, BP CEO Hayward and US Energy Secretary Steven Chu monitored operations together in Houston.
BP Chief Operating Officer Doug Suttles said on Wednesday it appears drilling mud, not oil, was gushing from the ruptured undersea well six hours into an effort to halt a growing oil spill.
BP is also drilling relief wells that should stop the flow from the main well but they are not expected to be completed until August.
The London-based energy giant has estimated that about 5,000 barrels (210,000 gallons/795,000 liters) have been leaking every day, although some scientists have given much higher numbers.
