Live underwater video shows a new cap has been placed onto the leaking well in the Gulf of Mexico, offering hope of containing the gusher for the first time since BP's deepwater rig exploded in April.
BP officials did not immedietely comment Monday evening on the video images streamed online by the company.
The company has said the next step will be running tests to make sure there are no other leaks from the well. Tests and monitoring could last from six hours to two days.
The old cap, removed Saturday, did not have a tight fit and allowed crude to escape.
BP is drilling two relief wells so it can pump mud and cement into the leaking well for a permanent fix.
If the cap works, the blown-out well will still be leaking. But the newer, tighter cap will enable BP to capture all the oil and funnel it up to ships on the surface.
Live: Watch BP's Attempt to Cap the Well
One of those ships, the Helix Producer, began operating Monday and should be up to its capacity of collecting roughly 1 million gallons of oil a day within a few days, Chief Operating Officer Doug Suttles said.
A permanent fix will have to wait until one of two relief wells being drilled reaches the broken well, which will then be plugged up with drilling mud and cement. That may not happen until mid-August.
BP's confidence in the cap is growing, Suttles said at a Monday news briefing. But he struck a cautious note, after a series of failed attempts by the company to contain the leak since the April 20 oil rig explosion that killed 11 workers and triggered the spill.
"Until we have the cap on, securely fitted in place, and know it's operating per the design, we have to recognize this is a complex operation," Suttles said.
Of particular concern is the potential for ice-like crystals, or hydrates, that could build up inside the cap where it connects to the well.
Engineers are spraying a chemical that acts as an antifreeze, concerned that if the crystals start forming they will compound and clog the piping. They do not want the flow of oil to stop instantaneously, said Don Van Nieuwenhuise, director of Professional Geosciences Programs at the University of Houston. Shutting the oil off too quickly could cause another explosion, he said.
"Rather than like a train running into a brick wall, it'll be more like putting the brakes on slowly," he said. "That's what they're aiming for. You can keep the brakes on and everyone arrives alive, or you hit the wall and have big problems."
Meanwhile, the U.S. Interior Department formally issued a new offshore drilling moratorium late Monday, saying it would end by Nov. 30 or sooner and it would no longer be based on water depths.
"A pause on deepwater drilling is essential and appropriate to protect communities, coasts, and wildlife from the risks that deepwater drilling currently pose," Interior Secretary Ken Salazar said in a statement.
"I am basing my decision on evidence that grows every day of the industry's inability in the deepwater to contain a catastrophic blowout, respond to an oil spill, and to operate safely," he added.
Gulf Residents Watch Closely
Work on the new capping operation began Saturday with the removal of a leaky cap that captured about 1 million of the 1.5 million to 2.5 million gallons of oil the government estimates is spilling from the well every day. The removal of the cap allowed oil to gush unhindered into the Gulf again.
The new cap was designed to snap into place on top of another piece of equipment installed overnight. BP said that once it is securely fastened, it will be tested by shutting off vents — perforations in a pipe that allow oil to flow out the top.
Engineers will be watching pressure readings. High pressure is good, because it would mean the leak has been contained inside the wellhead machinery. But if readings are lower than expected, that could mean there is another leak elsewhere in the well.
"Another concern right now would be how much pressure the well can take," and whether intense pressure would further damage the well, said Eric Smith, associate director of the Tulane Energy Institute.
Gulf residents closely watched the operation, knowing the damage already done to the biologically rich Gulf and the coast's two leading industries, fishing and tourism.
"I think we're going to see oil out in the Gulf of Mexico, roaming around, taking shots at us, for the next year, maybe two," said Billy Nungesser, president of Louisiana's oil-stained Plaquemines Parish. "If you told me today no more oil was coming ashore, we've still got a massive cleanup ahead."
BP "can't do much, but they know how to drill wells," dock master Jimmy Beason said at a marina in Orange Beach, Ala. "I think that by the end of the month it will be stopped, and this work with the cap is part of it. I see the light at the end of the tunnel."
As of Monday, between 89 million and 176 million gallons of oil had poured into the Gulf, according to government estimates.