This is not necessarily true. At one time, fossils were discovered adjacent to coal deposits, which gave us the misnomer "fossil fuels." However, it has been observed that some abandoned oil fields have refilled. Some speculate that the heat and pressure within the earth's crust is capable of reforming inorganic carbon into hydrocarbons.
That is a fringe theory, definitely not a valid one among the GW acolyte crowd, which the previous poster is addressing.
In this article, Freeman Dyson gives a brief description of Thomas Golds theory on the non-biological orign of oil, and recent results that tend to back up that possiblity.