BP also cautioned that while the well integrity test

To get the information To get the information, BP is taking what some view as the risky step of shutting in the well, using robot submarines to close valves on a huge capping stack that was lowered onto the well the day before.

"Simply shutting the well in and hoping that pressure doesn't rise too much is like playing Russian roulette with five bullets in the gun," analysts with Tudor, Pickering, Holt & Co. Securities told investors Tuesday.

But BP officials said steel casing inside the well is strong enough to withstand the spike in pressure and that the test can be aborted if there appears to be a risk of rupturing the well.

"The test has been carefully designed to make sure we don't create a bad situation," said Kent Wells, a BP senior vice president, during a technical briefing Tuesday afternoon.

BP also cautioned that while the well integrity test should stop the flow of oil out of the well for hours and possibly days, it is still a temporary fix until a relief well intercepts the Macondo near its source and permanently plugs it with mud and cement. The company says August remains the target for that procedure.