A lot is riding on British Petroleum as crews work to carry out the 'top kill' maneuver.

The technique involves shooting thousands of pounds of heavy mud into a five-story stack of pipes to clog the well.

Experts say it could take anywhere from a few hours to two days to determine whether the top kill is working and have given it a 60% to 70% chance of working.

The method is routinely used above ground, but has never been tried at 5,000 feet beneath the water.