So… every geologist who searches for oil on the hypotheses that it is the remnant of an ancient algae blooms in a shallow inland seas is wrong? Okay…
To make oil you need 1) carbon and 2) hydrogen. What reaction within the Earth would provide those elements while not also producing oxygen? There isn't one.
> while not also producing oxygen?
>why?
Because then the oxygen would promptly react with the newly created oil and consume it.