The early Earth was made of the same stuff as comets and asteroids, so the presence of hydrocarbons deep within the Earth is to be expected. It used to be thought that the fierce heat deep underground was sufficient to break up any hydrocarbon molecules. However, Russian scientists have demonstrated that the enormous pressures prevent this. Even if the Earth did not manage to retain its original supply of hydrocarbons it is likely that the rain of comets, space dust and asteroids over billions of years would have kept the crust of the Earth topped off with the raw ingredients for oil. Oil is best found near impact structures.
Oil forms deep underground from non-biological processes.
If these ideas prove correct then Donofrio's estimates for the United States should apply to other parts of the world. For areas of similar size there are possibly 20 buried impact craters with perhaps half having commercial oil reserves. The search for these elusive craters could be very rewarding. It may turn out that there is too much oil for our own good. A massive increase in known oil reserves could lower oil prices and drastically devalue existing reserves.