it's BP, Transocean and Halliburton ( had to look it up as I didn't even really remember )
the way it was explain to me ( a dummy ) was ...well - I tried to illustrait it but prolly not as well as my friend did

Basically there are 4 safe guards in place, each company was responsible for a safe guard.
That thing at the bottom is the oil pipe.
item #1. These are pipes that connects to a rig, these pipes should have been maintained and kept up to code, because they were not maintained the oil burst through them ... in the picture I drew them strait, but they are actually in such bad chape that they are bent at a 45 degree angle ( or that's what she told me )
item #2. There are three large chambers that are suppose to close and keep the oil from leaking into the pipes above - but the system failed and none of the chambers closed - they are investigating why
item #3. These are sensory pipes that keep the oil from over filling and getting dumped into the ocean, once the tubes sense the oil filling up the tube, it allerts the chambers at the bottom to close. But it didn't happen - they are investigating why
item #4. There is a large chamber at the bottom that opens and closes, this is how they control the oil pressure and flow. This chanber did not close properly and pressure from below forced it open even more.