Who is responsible for The Louisiana oil spill?

The British Petroleum Corporation, has overall responsibility as they are have exploration rights to the block where the well is drilled, and is the operator of the well.

Now, there is likely to be disagreement to who caused the well to blow out. The blow out preventers did not operate as they should. So, the owners of the rig, Transocean Corp, and the makers of the blow out preventers, Cameron, may be connected to the cause of the spill. Finally, the blowout occurred shortly after cementing in production tubing, done by Halliburton, so their actions may also be related to the accident.