According to Lindsey Willaims:

BP drilled a super well down to 25,000 to 20,000 feet in the gulf, much like Russia did on land.
They hit oil (a Biotic fuel that is not fossilised fuel like before) that is gushing out at a pressure of 20,000 to 70,000 PSI, which took them by surprise, and the security measures they have, cannot cope with the pressure.
They are preparing to evacuate the area, just in case they cannot come up with solutions to contain it.