A pivotal moment in the Gulf oil crisis was derailed Tuesday evening when officials announced they needed more time before they could begin choking off the geyser of crude at the bottom of the sea.

BP and government officials did not say what prompted the decision or when the testing on the new, tighter-fitting cap would begin.

The oil giant was scheduled to start slowly shutting off valves on the 75-ton metal stack of pipes and valves Tuesday, aiming to stop the flow of oil for the first time in three months.

If the cap works, it will enable BP to stop the oil from gushing into the sea, either by holding all the oil inside the well machinery like a stopper or, if the pressure is too great, channeling some through pipes to as many as four collection ships. The operation to close the valves could take anywhere from six to 48 hours.

A series of methodical, preliminary steps has been completed, including mapping the sea floor.

Late Tuesday, National Incident Commander Thad Allen met with the federal energy secretary and the head of the U.S. geological survey and other scientists and geologists.

"As a result of these discussions, we decided that the process may benefit from additional analysis that will be performed tonight and tomorrow," Allen said.

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