Eighty-four days into the oil spill, British Petroleum is once again trying to replace the cap and contain the leak in the Gulf of Mexico once and for all.

Over the weekend, the company removed the old cap sitting atop the well. BP's remotely controlled underwater robots are working to replace it with a new 100-ton capping system that would be bolted and sealed, which will allow less oil to escape.

The installation is risky, because crude oil is spilling into the Gulf unchecked during the cap exchange. However, there are now twice as many skimming boats cruising above the leak.

BP says it will be several days before it knows if the new cap will capture all of the crude spewing from the gusher one-mile down on the ocean floor.

Hopes remain high that the procedure will work.

"We think there is a very, very good chance that this will provide the kind of relief that we need," said White House Senior Advisor David Axelrod.

Meanwhile, BP says it's still too early to estimate a final cost for the oil spill. So far, the U.S. Securities and Exchange Commission has estimated the spill's costs to be around $3.5 billion.