The plan to start choking off oil gushing into the Gulf of Mexico was suddenly halted as government officials and BP said further analysis must be done Wednesday before critical tests could proceed.
No explanation was given for the decision, and no date was set for when testing would begin on the new, tighter-fitting cap BP installed on the blown-out well Monday.
In the meantime, oil continued spewing into the Gulf.
The oil giant had been scheduled to start slowly shutting off valves Tuesday on the cap, aiming to stop the flow of oil for the first time in three months. BP was initially ahead of schedule on its latest effort to plug the leak. The cap was designed to be a temporary fix until the well is plugged underground.
A series of methodical, preliminary steps were completed before progress stalled. Engineers spent hours on a seismic survey, creating a map of the rock under the sea floor to spot potential dangers, like gas pockets. It also provides a baseline to compare with later surveys during and after the test to see if the pressure on the well is causing underground problems.