Quality matters, not quantity. That was the message from the International Energy Agency (IEA) in its latest Oil Market Report. The world has plenty of oil, but perhaps not the right type of oil. A series of events have caused the market for light oil to diverge from that of medium and heavier blends. This trend has been underway for some time, but the deviation has magnified recently, and could cause havoc as 2019 wears on. The backdrop is the surge in U.S. shale production. The multi-year boom in light sweet oil from Texas and North Dakota, among…