Kent Wells, BP PLC vice president, said at a Friday news briefing that pressure is good inside the new cap.
Wells spoke 17 hours after valves were shut to trap oil inside the cap, a test that could last up to 48 hours. He said there were no signs of any new leaks underground.
Engineers are looking for high pressure in the cap because low pressure would be a a sign of another leak.
BP is also planning to start drilling again on a relief well, part of the permanent fix of plugging the well at the bottom.