BP was encouraged Saturday as the final hours ticked away on a two-day trial run of a massive cap on its busted Gulf of Mexico well, saying there no signs of new leaks and oil was being kept out of the water.

Kent Wells, a BP PLC vice president, said there was no evidence from an array of pressure, temperature, sonar and other readings that oil was escaping through the sea floor or anywhere else in the well.

A new breach underground was a major concern going into the test, because oil breaking through the sea floor would be harder to control and could endanger plans for a permanent underground plug.

"We're feeling more comfortable," Wells said on a conference call, but cautioned: "The test is not over."

Wells said there has been no decision yet on whether they will reopen the cap and let oil back into the water when the 48-hour test period ends Saturday around 3:30 p.m. EDT.

That call will be made by the Obama administration's point man for the disaster, retired Coast Guard Adm. Thad Allen, Wells said.

BP shut valves in the cap Thursday, stopping the flow of oil into the Gulf for the first time since the April 20 explosion on the BP-leased oil rig Deepwater Horizon killed 11 workers and unleashed the spill 5,000 feet below the sea.

With the cap working like a giant cork to keep the oil inside the well, scientists kept watch in case the buildup of pressure underground caused new leaks in the well pipe and in the surrounding bedrock that could make the disaster even worse.

Pressure readings after 41 hours were 6,745 pounds per square inch and rising slowly, Allen said, below the 7,500 psi that would have shown the well was not leaking. He said pressure continued to rise between 2 and 10 psi per hour. A low pressure reading, or a falling one, could mean the oil is escaping.

Wells also said the oil giant was making progress on its more permanent solution, a relief well that will be used to plug the leak with a mixture of mud and cement.