In the last six months the price of oil has collapsed dramatically. It has been called an oil shock. Previous oil shocks have had profound and long-lasting effects. No single commodity is more important to the global economy – and therefore to global politics. What are the political consequences of cheap oil? Contributors include an ex-president of Shell Oil, a former US energy secretary and one of the world’s leading thinkers on the subject. (Image: Oil rig in the North Sea. Credit: Press Association)