Scientists say the well is gushing about 60,000 barrels a day.

Officials optimistic

Retired Coast Guard Admiral Thad Allan, who is overseeing efforts to tackle the leak, said the well could be totally contained, although not plugged, by Monday if the new cap works.

"When we have the cap on, and its sealed and we know we've got a seal, the oil will be contained," Allan said, adding that a timeline provided by BP was being reviewed. 

in depth

BP has made numerous attempts to plug and contain the blown-out well, which has been leaking oil into the Gulf since an oil rig exploded on April 20. 

Gregg McCormack, the director of the petroleum extension service at the University of Texas, said the cap "stands a good chance of working".

"There's very little real risk and ... a great reward if they're able to capture all of the oil and gas that's flowing right now," he told Al Jazeera from Michigan.

"If the process doesn't work, and they put the exisiting cap back on, then it'll be worse than it was before."

McCormack said the methods BP had previously tried were "not a perfect fit ... and made it [the oil spill] even worse than they had anticipated".

"There was a lot of oil flowing out underneath the cap. Now this new cap is going to be bolted down and so there's no possibility that oil and gas can escape further," he said

Relief wells

Since the spill began, millions of barrels of crude have polluted coastlines in all five US Gulf states and wreaked havoc on wildlife and ecosystems in the area.

The leak is expected to continue until mid-August, when two relief wells are to be completed.

Engineers are optimistic the new cap will contain all the leaking oil [AFP]

But if all the oil spilling into the sea can be contained, the disaster - already the worst in US history - should not get any worse.

The spill has become a major political issue in the US, complicating Washington's relationship with Britain and putting Obama under domestic pressure over his handling of the disaster.

His administration said on Friday that it would annouce a new moratorium on deep water oil drilling after US courts failed to extend an existing six month ban on drilling below 152.5 metres.

Opponents of the ban warn that it is too broad and could force multinational oil companies to withdraw from US waters, threatening jobs in an uncertain economic climate.

News that the worst of the spill might be over has given hope to investors who have watched BP's share price plummet as the crisis has developed.

The past two weeks have seen BP's shares gain 25 per cent in value as rumours that the energy giant is seeking new investors gave hope that the company would recover from the crisis.