BP robots have attached a new, tighter-fitting cap on top of the Gulf of Mexico oil well, raising hopes it can finally fully stem the flow of crude for the first time in nearly three months.

The British energy giant said in a statement it had installed the 40-ton containment device on the sea bed more than one and a half kilometers beneath the surface.

The cap will be tested by closing off three separate valves that fit together snugly, choking off the oil and blocking it from entering the Gulf.