New Orleans: US officials delayed a make-or-break test on the integrity of the leaking Gulf of Mexico oil well so further checks could be carried out on the procedure.
The former Coast Guard chief leading the US response to the disaster took the decision to put the test off until at least Wednesday after meeting Energy Secretary Steven Chu, a Nobel Prize-winning physicist, and other top experts.
"As a result of these discussions, we decided that the process may benefit from additional analysis that will be performed tonight and tomorrow," Admiral Thad Allen said in a statement.
BP is poised to test whether a huge 75-tonne cap can seal the leak without threatening the structural integrity of the well.
The device, which contains three giant valves, was lowered late Monday and latched onto the ruptured pipe almost a mile down on the sea floor where only underwater robots can operate.
Once given the go-ahead, BP engineers will gradually close the valves on the cap and shut down the flow of oil in a process expected to last between six and 48 hours.
But US officials fear that if the pressure caused by closing the valves increases too quickly the cap could send oil shooting up from a new leak on the sea floor.
BP put out a statement shortly after Allen, confirming the test had been put off until more checks could be done.
"This analysis will be conducted tonight and into tomorrow. Consequently, the well integrity test did not start today," the statement said.
Once the test gets under way, fingers will be crossed in the hope of high pressure readings which would mean there are no other leaks and the valves on the cap can remain closed to effectively seal the well.
Low pressure would indicate oil is seeping out of the external casing of the well, meaning the valves would have to be reopened to reduce the risk of a new gusher on the seabed. Containment operations would then have to resume.
"The worst-case scenario is that it could actually broach back to the sea floor," explained senior BP vice president Kent Wells.
"Everybody hope and pray that we are seeing high pressures here," he said. "If the tests confirm that we can shut in the well, then the well will obviously be shut in and there will be no leakage into the sea."
Scientists will receive pressure readings every 12 seconds and relay the information to BP and government experts, including Allen and Chu, who was dispatched by US President Barack Obama to oversee the crucial decision-making for this pivotal moment in the 85-day disaster.
Allen said earlier that pressure readings anywhere between 8,000 and 9,000 pounds per square inch would indicate that the casing of the wellbore, which extends 2.5 miles (four kilometers) below the sea floor, is secure.
That would be good news for the Gulf residents who have seen an estimated 35,000 to 60,000 barrels of oil spewing into the sea daily since an April explosion destroyed a BP-leased drilling platform off Louisiana.
Tar balls and ribbons of crude have washed up along all five Gulf states, from Texas to Florida, shutting down key fishing grounds and scaring away tourists.
An estimated 2-4 million barrels of crude have gushed into the sea since the BP-leased Deepwater Horizon sank on April 22, two days after an initial blast which killed 11 workers.
Despite the endgame underway in the Gulf, there was little optimism at a presidential commission hearing into the causes of the disaster as victims struggled to come to terms with the damage.