This is the first I've heard of this theory, and it's interesting... some scientists believe that crude oil isn't the product of decomposed plant and animal matter from prehistoric times; rather they believe it is the product of a natural, inorganic process that takes place at the very hot interface of the earth's crust and mantle.
Some oil reservoirs tend to refill over time, often from the bottom up, implying a seepage from a larger reservoir underneath. The observations and the science seem to support the theory, as well as filling a few holes in the decayed animal/plant matter theory... such as the question of why large oil fields are sometimes found in areas where it is unlikely that a lot of life was present in prehistory. Here's a
news story. If you prefer your science hard, read
this.
If this theory is accurate, that would mean that oil is not the limited resource it is currently regarded as; or, the limit is much higher than current estimates, by perhaps 100 times. Oil is still a dirty fuel, and a cleaner alternative would be beneficial, but maybe the oilfields won't by drying up as soon as we think.