Published: May 11, 2010 9:21 PM EDT

ON THE GULF OF MEXICO  - A BP spokesman says a second, smaller oil containment box known as a "top hat" is being brought to the site of a blown-out well in the Gulf of Mexico.

Spokesman Bill Salvin tells The Associated Press the box will be lowered to the seafloor, away from the plume, on Tuesday. He says undersea robots will position it over the gusher by Thursday.

The box is on a vessel in the containment zone right now. More than 4 million gallons of oil have spewed from the well since the Deepwater Horizon drilling rig exploded April 20.

If crude keeps spilling at the current rate of 210,000 gallons a day, it will eclipse the Exxon Valdez disaster by Father's Day.