Nothing lasts forever, not even oil. The world does not have an infinite amount of oil, which is bad news since oil is the most cost effective form of energy on the planet. Peak Oil, the point where we've extracted 1/2 of the world's supply, has severe economic implications. Oil is used not just to produce gasoline but also in plastics, medicine, and fertilizer. We can't grow food on a large scale like we do today without oil. The world will change without oil and so will investment strategies. Here's what you need to know about Peak Oil investing.