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.”

BP finished pumping cement into its ruptured oil well in the Gulf of Mexico on Thursday to seal off the source of the world’s worst offshore spill, paving the way to permanently plug the blow-out later this month. The daylong cementing operation followed earlier injections of heavy drilling mud this week that had subdued the upward pressure of oil and gas inside the deep-sea Macondo well. The crippled wellhead was provisionally capped in mid-July. “This is not the end, but it will virtually assure us that no oil will be leaking into the environment,” retired Coast Guard Admiral Thad Allen, who oversees the U.S. oil spill response operation, said at a briefing in Washington. “Monitoring of the well is under way in order to confirm the effectiveness of the procedure,” BP said in a statement announcing completion of the cementing work.

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.

Oil is no longer spewing into the Gulf of Mexico — at least temporarily — as BP Plc said it choked off the flow from its undersea well that ruptured in April and caused the worst offshore oil spill in U.S. history. BP said it stopped the leak on Thursday with the tight-sealing containment cap installed three days earlier atop its blown-out well, and awaited on Friday the results of tests on whether the well remains intact. That’s a key issue as the British energy giant moves to plug the leak permanently with a relief well intended to intersect the ruptured well — which extends 2.5 miles under the seabed — and seal it with mud and cement next month.

BP Plc on Tuesday delayed a critical test that will determine if it can close a cap atop its ruptured Macondo well that has leaked oil into the Gulf of Mexico for the last 12 weeks. The British energy giant and U.S. authorities said they were postponing the test that had been scheduled for Tuesday to establish whether the well can withstand the pressure caused by closing the cap at the wellhead. “We decided that the process may benefit from additional analysis that will be performed tonight and tomorrow,” retired Coast Guard Admiral Thad Allen, who is overseeing the U.S. response to the spill, said in a statement. The tests, due to last between six and 48 hours, had been scheduled for late Tuesday on BP’s newly installed “capping stack,” which has a better seal than the last cap placed on the well and aims to stop oil from spewing out of the failed blowout preventer.

“Some 3,000 years ago, farmers in eastern China domesticated the soybean. In 1765, the first soybeans were planted in North America. Today the soybean occupies more US cropland than wheat. And in Brazil, where it spread even more rapidly, the soybean is invading the Amazon rainforest,” writes Lester R. Brown, president of the Earth Policy Institute, in a December commentary.