BP lowers cap onto leaking oil well in Gulf of Mexico
Oil firm BP has lowered a cap onto a leaking oil well in the Gulf of Mexico, in the hope of piping some of the oil to ships on the surface.
Video footage showed the cap lowered into place against pressure from escaping oil and gas. It could be 24 hours before it is clear whether the move has worked.
It is the latest effort by BP to stop the leak, but as David Shukman explains, it is a process which has not been tried before.