Retired Coast Guard Admiral Thad Allen said: 'We basically have secured this well. We have essentially eliminated the threat of discharge from the well at this point.'
A cap on top of failed blowout preventer equipment on the Macondo well had sealed in all oil flow since 15 July.
BP replaced the failed equipment on Friday with a new giant stack of valves and pipes.
Once the new blowout preventer is tested, BP can resume drilling a relief well that will bore into the Macondo well and pump in mud and cement to plug it for good.
'We should be ready to move forward with the relief well sometime next week,' Adm Allen said.
A blowout preventer (BOP) is designed to shut off all flow and contain pressure if oil or gas leak uncontrollably from a seabed well.
The Macondo BOP failed on 20 April, leading to an explosion on the Deepwater Horizon drilling rig that killed 11 men.
The well spewed more than 4m barrels of oil into the Gulf of Mexico over nearly three months.
