With a final shot of cement, BP Plc permanently “killed” its deep-sea well in the Gulf of Mexico that ruptured in April and unleashed the worst oil spill in U.S. history, the top U.S. spill official said on Sunday.

Some 153 days after the Macondo well ruptured, the U.S. government confirmed that BP had succeeded in drilling a relief well nearly 18,000 feet below the ocean surface and permanently sealing the well with cement.

“The Macondo 252 well is effectively dead,” retired Coast Guard Admiral Thad Allen, who has overseen the U.S. government’s response, said in a statement. “We can now state, definitively, that the Macondo well poses no continuing threat to the Gulf of Mexico.”