That leaves three options: They can keep the well shut, they can open it temporarily or permanently, or they can do nothing and continue to keep vigil over the bandaged well for some new sign that convinces them it is stable enough to deem the cap a success.
BP's vice president Kent Wells said engineers have been constantly monitoring pressure, temperature and sonar sensors and have not seen any evidence of oil escaping into the water or the sea floor. Submarine robots are also patrolling the well for signs of leakage.
A possible new underground breach was a major concern with the new lid, because oil breaking out of pipes in the bedrock would be harder to control and could endanger plans for a permanent plug.
Wells said Saturday morning that BP is feeling "more comfortable," but the company is cautious to make any premature announcements.
Then, as the deadline passed Saturday afternoon, the company made no further statement. Even if the well stays plugged, it will take months, or possibly years for the Gulf to recover.
BP shut valves in the cap Thursday, stopping the flow of oil into the Gulf for the first time since the April 20 explosion on the BP-leased oil rig Deepwater Horizon killed 11 workers and unleashed the spill 5,000 feet below the sea.
- Authorities said pressure readings after 41 hours were 6,745 pounds per square inch and rising slowly. The pressure continued to rise by around 2 psi per hour. A low pressurereading, or a falling one, could mean the oil is escaping.
- The cap is a temporary measure until a relief well can be competed and mud and cement can be pumped into the broken well deep underground to seal it more securely than the cap. The cap is designed to prevent oil from spilling into the Gulf, either by keeping it bottled up in the well or by capturing it and piping it to ships on the surface. It is not yet clear which way the cap will be used if it passes the pressure test.
- There are two relief wells in the works. Wells said work on the first one was far enough along that they expect to reach the broken well's casing, or pipes, deep underground by late this month. Then the job of jamming it with mud and cement could take "a number of days through a few weeks."
- Even with the cap holding, no one has declared victory - or failure. President Barack Obama on Friday cautioned the public "not to get too far ahead of ourselves," warning of the danger of new leaks "that could be even more catastrophic." BP and government scientists at sea and in a faraway control room at BP's U.S. headquarters in Houston have been keeping a vigil around the clock since the cap was shut.
The Associated Press contributed to this report.