(4)
Looks like it was their incompetence in their cementing process.
It was their cementing that allowed the methane to seep thru causing the explosion. Granted, working with cement at those depths causes many problems not encountered at shallower depths. All the more reason to have "all" recommended safety features installed. BP's decision to not spend that measly $500,000 on that acoustic BOP device now looks very, very short sighted.
Cementing contributed to half of the 39 U.S. blowouts between 1992 and 2006, according to a report that Danenberger co-authored in 2007.
(4) Intentionally disingenuous spins on already established facts. Seriously