Vessels work the late shift above BP's Macondo wellhead, source of the Gulf of Mexico oil spill, on Tuesday, one day after a new oil-containment cap had been fitted to the gushing pipe a mile (1.6 kilometers) below. (See Gulf of Mexico map.)
Thursday afternoon BP announced the new cap had been fully sealed during a crucial "integrity test" and that oil had completely stopped leaking from the site for the first time since the Deepwater Horizon oil rig exploded and sank on April 20.
The welcome development comes after a roughly 24-hour delay, during which experts scrambled to allay U.S. government scientists' fears that the test could further damage the well.
"This last minute evaluation was due to an overabundance of caution," said Coast Guard admiral and response-team leader Thad Allen in a press briefing Wednesday evening. "We sat long and hard about delaying this test. This was not easy."
Thursday morning BP delayed the test one last time after workers had discovered a leak in the so-called choke line, which allows oil from the cap to be siphoned to the surface.
But, BP Senior Vice President Kent Wells told reporters early Thursday, "fortunately we had a second choke on surface ... and we're once again going through the process of positioning ourselves to do the well integrity test."
BP's integrity test should determine whether the new oil cap can remain sealed without causing a dangerous buildup of pressure in the well.
(Related: "Gulf Oil Spill Worst in History; Drilling Postponed.")