The oil leak in the Gulf of Mexico could take until August to plug, according to BP, which is now drilling two relief wells in the latest attempt to stem the flow of oil.

This attempt follows BP’s ‘top kill’ operation at the MC252 well, which was intended to stem the flow of oil and gas and ultimately kill the well by injecting heavy drilling fluids through the blowout preventer on the seabed, down into the well.

Despite successfully pumping a total of over 30,000 barrels of heavy mud in three attempts at rates of up to 80 barrels a minute, the operation did not overcome the flow from the well, the company said in a statement.

BP will use a containment device known as a lower-marine riser package cap, a piece of equipment that sits on top of the failed blowout preventer at the seabed, one mile below the surface of the sea.

The well has so far leaked between 12,000 and 19,000 barrels of oil a day into the sea following the explosion and sinking of the Deepwater Horizon rig on 22 April.

The spill is now believed to the largest ever in US history and BP says its costs from the spill have hit about $940m.