OIl, oil toil and trouble
Incidentally, this chart from the Wall Street Journal is a very useful little history of oil prices. You can see what happened in the eighties, as demand sagged, and also the amazing run-up we've had over the last few years.
One of the things that I was struggling to get across at a dinner a few weeks ago is how discontinuous prices on inelastic goods can be. That is, a few percentage points increase in demand against a relatively fixed supply doesn't produce a few percentage points increase in price: it can produce huge spikes. That's not intuitive; we feel as if prices and demand should grow at approximately the same rate. But people in the world have a lot of spare income they can use to bid up the price of oil; the speed with which its price is increasing is a measure of just how useful the stuff is.