Britannica Sources used in this answer

When was the Deepwater Horizon well declared completely sealed?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Fireboats battle a blaze on the Deepwater Horizon drilling rig in the Gulf of Mexico, April 2010. — Deepwater Horizon oil spill Fireboat response crews attempt to extinguish the blaze aboard the Deepwater Horizon oil rig in the Gulf of Mexico, April 21, 2010.

The Deepwater Horizon well was officially declared completely sealed on September 19, 2010, following the successful execution of a "bottom kill" procedure and a series of subsequent pressure tests.1