Heinz-Peter Bader/ReutersIt was only a few months ago that OPEC, once the de facto arbiter of oil markets, seemed to have a plan to inflate the price of oil: The cartel, along with several non-OPEC members, agreed in December to cut production by roughly 1.2 million barrels per day. And for the first quarter of 2017, OPEC largely made good on its pledge.