BP Plc extended for another 24 hours a critical test of its blown-out Gulf of Mexico well that so far has shut off the huge oil leak, the top U.S. official overseeing the spill response said on Saturday.

The British energy giant, which cut off the flow of oil from the deep-sea well on Thursday when it began the test to gauge its structural integrity, expressed growing confidence that the well was intact.

Kent Wells, BP’s senior vice president of exploration and production, said there was no evidence of any leaks. “We’re feeling more comfortable that we have integrity” in the well, Wells added, in what would be an important step toward permanently plugging it.