Now begins a waiting period to see if the cap can hold the oil without blowing a new leak in the well. Engineers will monitor pressure readings incrementally for up to 48 hours before reopening the cap while they decide what to do.
Though not a permanent fix, the solution has been the only one that has worked to stem the flow of oil since April. BP is drilling two relief wells so it can pump mud and cement into the leaking well in hopes of plugging it for good by mid-August.
BP has struggled to contain the spill and had so far been successful only in reducing the flow, not stopping it. The company removed an old, leaky cap and installed the new one Monday.
Between 93.5 million and 184.3 million have already spilled into the Gulf, according to federal estimates.