Really?  According to the majors, announcing serious layoffs (which appear to have been understated) this spring, "we waited to see if the decline was temporary, but it isn't" (paraphrase).  It was a combination of US production increases, repairs to the Iraqi industry (ongoing), the combination of legal exports by Iran with new investment in obsolete Iranian industry, and the major role of Russia that "conspired" with Saudi's policy to drive prices down.  Today both Saudi and Russia wish they could stop the drop - but they apparently lack control.   Control in a true market is difficult and very expensive for any one player.