Many of these (I'm not sure it was really 50 ??) had to be shut down due to their age and the fact that it would have been too expensive to bring them up to code. Further, the economy of scale of newer refineries has made a lot of older, smaller places unprofitable. Same thing is happening in the chemical industry right now where new plants in the Middle East and China that are 4-5 times larger than many older plants are radically changing the economics. It's an interesting time.