Oil speculators.

Imagine that you bought 10 barrels of oil for $50 (like 3 yrs ago). You then turn around and bid $100 for a barrel. Why would you do that? Well put yourself in the shoes of the oil producing countries and companies. Someone offered you twice the going rate. What do you do say no? That would be stupid. So now that people are willing to pay for oil at $100 what is the price? Sure is not $50. It is the highest price someone is willing to pay...$100.

Now you have 10 barrels you bought at $50 that are now worth 100. You just made $1000 off $500. If you repeat, the price keeps increasing. You make more money.

You are now a speculator. Congratulations! Now go make some money.