Oil is found at depths as far down as five miles. As there were never dinosaurs buried that deep and given that oil only goes up in the strata, like a bubble in water, there must be other mechanisms producing it than dead dinosaurs. Oil wells that were played out in the ‘40’s are producing again, so we obviously don’t understand where oil comes from.
This article is several years old, but gives a pretty good overall view. It’s major fault is that it does not take fracking into account.
Most of the evidence is for biotic oil origins. There may be some abiotic oil, but as a practical matter, it does not matter much.
http://richardheinberg.com/richard-heinberg-on-abiotic-oil