The graph shows oil prices in real terms. In 1986 there was a large price collapse, and last autumn a small collapse. The graph show everything but a managed market, refuting the alleged managing power of OPEC. Prof. Hamilton's blog wonders why oil price does not show a scarcity bonus, according to which the price of a finite resource being depleted should rise at a percentage rate equal to the rate of interest.
Conaly's blog maintains that the market is characterized by cartels and long time lags to get new production to market, as well as long time lags in production declines. As a result, we have oscillating prices. Conaly predicts a price collapse somewhere in the future. He seems right, but who knows?