BP Senior Vice President Kent Wells said Friday that pressure was rising inside the cap stack as the oil giant continued testing its capped Gulf wellhead with no evidence so far that other leaks exist.

Wells said the pressure was up to 6.700 psi (pounds per square inch) inside the well’s capping stack. The company is looking to achieve an optimal 8,000 psi, which would indicate that no oil was being forced out through a leak and that the well was undamaged and able to withstand the pressure of the cap.

The well “integrity test” began Thursday after two days of delays, first as government scientists scrutinized testing procedures and then as BP replaced a leaking piece of equipment called a choke line.   Testing could go on for 48 hours.

BP, cautioned, however, that the oil cutoff isn’t likely to go beyond 48 hours. Once the tests are concluded, valves are expected to open to resume siphoning oil to two ships on the surface. Two more ships are due to join them in the coming weeks.

Though the new cap is a step toward ending the disaster, the well will still not be killed until the relief wells are completed later in the month or in early August.