During the last half of 2008, as the global economy ground to a halt, the price of oil fell from an all-time high of $145 a barrel to less than $40. If you had a place to store that cheap oil, you could make a lot of money when prices rebounded. Thus was born the booming demand for oil tankers, or any other place to stash low-cost crude. By January 2009, with prices still hovering around $50 a barrel, there were some 90 million barrels of crude in floating storage. The futures markets had entered something traders call contango, a fancy commodities term for the expectation that prices will rise in the future. All an oil trader with storage space has to do is sell a futures contract to lock in that higher price a few months down the road and then just sit on it. Some call that hedging. Others call it free money.