BP has begun an operation to fit a tighter cap over a leaking oil well in the Gulf of Mexico.
Underwater robots have taken off the existing dome to make room for the new sealing cap.
The new containment cap could allow all the leaking oil to be captured and siphoned to surface vessels.
It will take four to seven days to get the new cap on and in that time there will be nothing stopping the oil escaping, the BBC reports.
But Admiral Thad Allen of the US Coast Guard says the flow could be shut off by Monday.
An extra ship, the Helix Producer, will then start siphoning the oil to the surface.
An estimated 35,000 to 60,000 barrels of oil have been gushing out of the ruptured well each day, and the current containment system has captured around 25,000 barrels every 24 hours.
BP says the new cap and the addition of the Helix Producer containment ship will raise capacity to 60,000 to 80,000 barrels a day - in effect halting the leak that has caused an environmental disaster in the Gulf Coast.
No permanent solution is expected until the first of two relief wells is completed in order to inject drilling fluids into the gushing well and then seal it permanently with cement.
On Thursday BP said that operation was ahead of schedule.
The leak began after an explosion and fire aboard the Deepwater Horizon drilling rig on 20 April. The rig sank two days later.