Oil deposits are allegedly largely from the Carboniferous era and predates dinosaur be a lot of millions of years.
Or so I have read...
Did you ever notice that in a forest fallen trees that have been there where they fell for many years are just hollow outlines of their former selves?
We can only assume that they slowly “combusted”, turned to water vapor and CO2 and left behind but traces of their former selves over 100s and 1000s of years; how much of the plant growth was supposed to have been trapped underground to be compressed into crude over time?