Risky 'top kill' fails to stem oil spill

• Oil booms in Redfish Bay, in the Bird's Foot Delta of Louisiana, which is stained by the oil that is still washing ashore weeks after the Deepwater Horizon blast.

The company is now considering scrapping the initiative in favour of yet another method to contain the worst oil spill in US history.

The comments from BP PLC chief operating officer Doug Suttles were delivered amid increasing scepticism that the "top-kill" operation – which involves pumping heavy drilling mud into a crippled well 5,000ft underwater – would halt the leak.

This is the latest in a series of proposed solutions BP has tried – including a gigantic box placed over the leak and a tube inserted to siphon the oil away. Both ultimately failed.

The top kill began on Wednesday, and "to date it hasn't yet stopped the flow", Suttles told a media call at Port Fourchon. "What I don't know is whether it ultimately will or not."

If the top kill fails, BP would cut off the damaged riser from which the oil is leaking and cap it with a containment valve that is already resting on the seafloor. BP is already preparing for that operation, Suttles said.

Since the top kill began on Wednesday, BP has pumped huge amounts of mud into the well, at a rate of up to 2,700 gallons per minute, but it is unclear how much is staying there.

A robotic camera on the seafloor appeared to show mud escaping at various times during the operation. Yesterday, the substance spewing from the well appeared to be oil, experts said.

BP has also tried several times to shoot assorted rubbish into the well's crippled blowout preventer, to clog it up and force the mud down the well bore. That, too, has met with limited success.

US interior secretary Ken Salazar said officials were evaluating the next step. He said the relief wells being drilled were the ultimate solution, but something was needed to stop the spill until they were finished – estimated to be August.

"We're doing everything with the best minds in the world to make sure that happens," he said.

The spill began after the Deepwater Horizon drilling rig exploded on 20 April, killing 11 people. It is the worst spill in US history – exceeding even the Exxon Valdez disaster in 1989 off the Alaska coast – dumping between 18 million and 40 million gallons of oil into the Gulf of Mexico, according to government estimates.

Eric Smith, associate director of the Tulane Energy Institute, said yesterday that the top kill appeared headed for failure.

"They warned us not to draw too many conclusions from the effluent, but it doesn't look like it's working," he said.

BP had pegged the top kill's chances of success at 60 to 70 per cent. The company says the best way to stop the flow of oil is by drilling the relief wells.

Chris Roberts, a councilman in Louisiana's Jefferson Parish, said he was frustrated by BP's failures and perceived lack of transparency.

"We're wondering whether or not they're attempting to give everybody false hope in order to drag out the time until the ultimate resolution to it" – the completion of the relief wells, he said.

Meanwhile, Coast Guard and Minerals Management Service officials heard a sixth day of testimony during hearings into the disaster in Kenner.

David Sims, BP's drilling operations manager for exploration and appraisal in the Gulf of Mexico, testified he was aware of problems experienced by the Deepwater Horizon's drilling crew in the weeks and months leading up to the explosion. He said there were no serious problems the day the rig exploded.

Meanwhile, US president Barack Obama has visited the Louisiana coast to see the damage as he tried to emphasise that his administration was in control of the crisis

"I'm here to tell you that you are not alone, you will not be abandoned, you will not be left behind," he told people in Grand Isle, where the beach has been closed by oil and the anger was palpable.

"The media may get tired of the story but we will not. We will be on your side and we will see this through."

Obama, who is facing criticism that he responded too slowly to the environmental catastrophe in the Gulf of Mexico, assured Louisianians during his five-hour visit that they "will not be left behind" and that the "buck stops" with him.

Obama is caught in a tight spot: there is not much he can do about the well other than apply pressure to BP to get it right and put his best scientists in the room. The government has no deep-sea oil technology of its own. That fact is not lost on the people of Louisiana's coast, a hub of the US oil industry and now the site of the country's largest oil spill.

Billy Ward, a developer who had been building a gated fishing community, which is now on hold because of the spill, said Obama's visit was for show and that there was nothing the president could do.

"It's the unknown that's killing us," said Ward, who comes to Grand Isle with his family every weekend to stay in their beach house. "We don't know if it's going to be six months or six years before we get back to normal, if ever. All we can do is pray."