There are reports (h/t oddlots at iTulip) to the effect that Schlumberger Ltd, a respected international consulting firm, warned BP about incorrect procedures shortly before the accident, only to have them ignored. How much of this is accurate is unclear. It is known that Schlumberger staff left the rig only a few hours before the explosion, but there are inconsistencies -- the Reuters story states that they left on a BP helicopter, while the stories making the stronger claims say that the Schlumberger folks, after their advice was allegedly ignored by BP, ordered in one of their helicopters after BP told them to wait for the next scheduled flight. Whatever the case, it's being taken seriously by some, as evidenced by the relative performance of BP's and Schlumberger's stocks:
No surprise here; the possible implications of this could be very unpleasant for BP. It's worth noting, of course, that stories aren't always true, even if you do see them on the Internet; we'll have to see where this goes.