NEW ORLEANS — After five months, the oil well that had spewed thousands of gallons into the Gulf of Mexico is on the verge of being plugged once and for all. A relief well drilled nearly 2.5 miles beneath the floor of the Gulf of Mexico intersected BP's blown-out well, a prelude to permanently killing it, the U.S government said.

Retired Coast Guard Adm. Thad Allen, the government's point man on the oil spill, said in a statement that data shows the two wells are joined. The next step will be to pump mud and cement down through the relief well to seal the ruptured well from the bottom.

The final seal should happen by Sunday, five agonizing months after an explosion killed 11 workers, sank a drilling rig and led to the worst offshore oil spill in U.S. history.

The gusher was contained in mid-July after a temporary cap was successfully fitted atop the well. Mud and cement were later pushed down through the top of the well, allowing the cap to be removed. But the blown-out well cannot be declared dead until it is sealed from the bottom.

The April 20 blast sank the Deepwater Horizon rig and triggered the spill that eventually spewed 206 million gallons of oil into the Gulf. BP PLC is a majority owner of the well and was leasing the rig from owner Transocean Ltd.

The disaster caused an environmental and economic nightmare for people along hundreds of miles of Gulf shoreline from Florida to Texas. It also spurred civil and criminal investigations and cost gaffe-prone BP chief Tony Hayward his job.