BP Plc said tests on its Macondo well show no evidence of damage that would prevent the company from keeping the well sealed with equipment installed earlier this week.

About 40 hours of data from pressure tests, seismic surveys and temperature gauges indicate the structural integrity of the well may be intact and the amount of oil in the reservoir is being depleted after three months of flowing into the Gulf of Mexico. There is no evidence of hidden leaks, Kent Wells, BP?s senior vice president for exploration and production, said on a conference call with reporters today.

?We have a tremendous amount of monitoring going on, and we?re very much focused on making sure that this test is run perfectly. We?re watching every piece of data,? Wells said. ?We feel more comfortable that we have integrity.?

Pressure inside the well rose slowly to 6,745 pounds per square inch from 6,700 pounds per square inch at the start of the day yesterday, an encouraging sign that the inside of the well may have escaped damage following an April 20 explosion aboard the Deepwater Horizon drilling rig, Wells said.

BP stopped the flow of oil to begin testing on the afternoon of July 15. The company, based in London, may decide to prolong the tests beyond the 48 hours initially planned, Wells said.

In a nail-biting day across the Gulf Coast, engineers struggled to make sense of puzzling pressure readings from the bottom of the sea Friday to determine whether BP’s capped oil well was holding tight. Halfway through a critical 48-hour window, the signs were promising but far from conclusive.

Kent Wells, a BP PLC vice president, said on an evening conference call that engineers had found no indication that the well has started leaking underground.

“No news is good news, I guess that’s how I’d say it,” Wells said.

Engineers are keeping watch over the well for a two-day period in a scientific, round-the-clock vigil to see if the well’s temporary cap is strong enough to hold back the oil, or if there are leaks either in the well itself or the sea floor. One mysterious development was that the pressure readings were not rising as high as expected, said retired Coast Guard Adm. Thad Allen, the government’s point man on the crisis.

Allen said two possible reasons were being debated by scientists: The reservoir that is the source of the oil could be running lower three months into the spill. Or there could be an undiscovered leak somewhere down in the well. Allen ordered further study but remained confident.

“This is generally good news,” he said. But he cautioned, “We need to be careful not to do any harm or create a situation that cannot be reversed.”

He said the testing would go on into the night, at which point BP may decide whether to reopen the cap and allow some oil to spill into the sea again.

Throughout the day, no one was declaring victory  or failure. President Barack Obama cautioned the public “not to get too far ahead of ourselves,” warning of the danger of new leaks “that could be even more catastrophic.”

Even if the cap passes the test, more uncertainties lie ahead: Where will the oil already spilled go? How long will it take to clean up the coast? What will happen to the region’s fishermen? And will life on the Gulf Coast ever be the same again?