ROBERT, La. (AP) - BP now says it will likely be at least Tuesday before engineers can shoot heavy mud into a blown-out well spewing oil into the Gulf of Mexico.

Three ultra-deepwater rigs and other equipment are at the site where the Deepwater Horizon oil platform exploded April 20. They're preparing for a delicate procedure called a "top kill" that BP hopes will stop the flow of oil from the well.

Crews will pump in heavy drilling mud, which is a thick, viscous fluid that's twice the density of water. That should stop the oil, and then they'll use cement to keep more from gushing out.

BP's Doug Suttles says this hasn't been tried at 5,000 feet underwater before, so engineers want to make sure everything is just right.