How do you cap a deep oil spill?

A deep water blowout is difficult to cap. In the gulf spill, BP tried to shut in the well by sending remotely operated vessels to actuate the blow out preventer (located in 5,000 ft of water). This did not succeed.

Presently, BP is drilling two relief wells which they will use to connect with the blown out well and pump mud down the wellbore of the blown out well. The added pressure of the mud is used to kill the influx of oil from the reservoir. The pressure added from the weight of the mud column must be more than the oil pressure being exerted from the reservoir.

See related link.