I think the problem is that demand for oil can change way more quickly than supply. At peak everybody was investing in production capacity and increasing produc

I think the problem is that demand for oil can change way more quickly than supply. At peak everybody was investing in production capacity and increasing production to profit from the high prices. Now demand has slipped (for example China), it's difficult to scale back production and supply exploded (fracking, and the Saudi-Iranian competition for market share).