"Nobody has yet synthesized crude oil or coal in the lab from a beaker of algae or ferns. A simple heuristic will show why such synthesis would be extremely unlikely. To begin with, remember that carbohydrates, proteins, and other biomolecules are hydrated carbon chains. These biomolecules are fundamentally hydrocarbons in which oxygen atoms (and sometimes other elements, such as nitrogen) have been substituted for one or two atoms of hydrogen. Biological molecules are therefore not saturated with hydrogen. Biological debris buried in the earth would be quite unlikely to lose oxygen atoms and to acquire hydrogen atoms in their stead. If anything, slow chemical processing in geological settings should lead to further oxygen gain and thus further hydrogen loss. And yet a hydrogen “gain” is precisely what we see in crude oils and their hydrocarbon volatiles. The hydrogen-to-carbon ratio is vastly higher in these materials than it is in undegraded biological molecules. How, then, could biological molecules somehow acquire hydrogen atoms while, presumably, degrading into petroleum?"
And from the above link...
Countries With Hydrocarbon Finds In Basement Reservoirs
The reservoirs are organised by continent
Europe
North America
South America
Asia
Africa
CIS and Russia
Middle East
Oceania
Under CIS and Russia: "...more wells have been drilled into crystalline basements within the FSU than all other nations combined with the consequence of greater production. For example, the Caspian district has a total of eighty fields producing from crystalline basements. Unlike the majority of drilling operations which cease as soon as basement rocks are encountered (Aguilera, 1995b), Krayushkin et al (1994) state that all of the hydrocarbon fields within the FSU producing from crystalline basements were developed intentionally."
Whatever natural processes are involved, they have not suddenly ceased because mankind decided to plant wheat, build cities, eat McDonalds, or drive SUVs. Therefore, oil is still being created.
Whatever process creates/raises oil, the question is, is it happening faster or slower than we are using it?
"Isoprenoids:
Pristane and phytane are the two predominant isoprenoids found in petroleum products. They are, in essence, "chemical fossils" from the hydrolysis of chlorophyll and tend to degrade after the straight chain aliphatics. "
The implication is that petroleum contains traces of biotic chemicals, obviating abiotic origins. Other sites mention isotopic ratios as proof of non-abiotic origin.
Perhaps the whole question is a false dichotomy. 'Organic' chemistry appears throughout the solar system, even in places we assume have no life. There may be biotic and abiotic origins to our subterranean hydrocarbon deposits.
Personally, I believe that the petroleum company geologists must have the best appreciation for this murky field. Their corporations have spent more and conducted more surveys and tests than all the universities and governments combined. Unless they are lying I trust their assessment.
(Are they lying?)