For a third day BP held back the oil. The pressure in the well is still rising slowly and BP now says the cap could remain closed for weeks until the well is sealed for good.
"Nobody wants to see oil flowing into the Gulf again," said BP COO Doug Suttles. "We're hopeful that if encouraging signs continue we may be able to keep the integrity test going until the point where we get the well killed."
That could be risky, reports CBS News correspondent Kelly Cobiella. With the oil held back, pressure is slowly building in the well bore and on the failed blowout preventer. If there's a weak point, the pressure could make it worse.
Tests have found no signs of leaks so far but the government's man in charge wants BP to keep looking. In a statement Thad Allen said, "We must ensure no irreversible damage is done which could cause uncontrolled leakage from the sea floor." And no one is ruling out the option of re-opening the valves and collecting oil again to avoid stressing the well.
"It would require oil flow into the Gulf of Mexico for up to three days but we just have to monitor this test minute by minute, hour by hour, day by day," said Suttles.
For nearly three months the thousands of workers at the command center have been trying to defend against the onslaught of oil. With BP's cap holding, their strategy is shifting from defense to offense.
BP's incident commander Mike Ustler says they use a map to see changes in the shape and size of the oil. "We are seeing it shrink and that's a wonderful feeling at this stage," he said.
Skimming boats and controlled burns are eating away at the oil on top of the water. Yet in the bays and marshes along the Gulf coast the damage is already done and biologists don't yet know how long it will take to recover.
Scientists say oil from other spills has stayed in the environment and affected marine life for decades but in some cases they say trying to remove every last drop from sensitive areas like marshes has done more harm than good.