The price of crude oil, like the prices of many other commodities, is volatile. Our first chart shows the price of a barrel of Brent crude since the early 1970s, adjusted for inflation. In real terms, oil prices, which had been broadly stable for more than a decade, rose by a factor of six between the late 1990s and the late 2000s, only to plummet as the global financial crisis hit, rebound as the recovery began, and fall sharply again...