BP Installs Sealing Cap on Errant Well

It could be another 48 hours before the company knows if the cap has entirely sealed the well. During that period, the company will perform a series of pressure tests to check the well's integrity. Concerns have been raised that the well could be even more damaged than previously known and that another uncontrolled leak could occur at any time.

The sealing-cap system hasn't been used before at these depths or conditions, BP said, adding that the system's "ability to contain the oil and gas cannot be assured."

But if all goes according to plan, BP's latest effort could finally bring the runaway well under control and make headway toward ending a saga that has cost the company billions of dollars and put it at odds with much of the American public and U.S. government.

"We have to recognize that this is a complex operation," said Doug Suttles, the company's chief operating office, during a teleconference early Monday. "Our confidence is growing."