1. "How then can "oil" be routinely discovered tens of thousands of feet down."
To the best of my knowledge, oil has never been discovered below 15,000.
Indeed, temperatures below 12,500 feet are generally above 275F (varies by your kneck of the woods), which breaks down hydrocarbons, giving you, if lucky, methane.
2. I am not discounting the possibility of abiotic hydrocarbons -- merely discounting the idea that the oil and gas we use is abiotic. (But, as stated in my first post, perhaps the reefs we use as markers may merely be capturing the hydrocarbons.)
Regardless of source, the reefs are there, which was the point of my post.
MeanWestTexan, PE (petro)
The question as to the origin of oil has always interested me as a microbiologist. Clearly coal is of plant origin, but oil is trickier. The presence of biological like compounds in oil does not have to show biological origin, the oil could have been contaminated at a later date. The presence of bacteria in almost all oil fields permits this possibility along with the possibility for underground migration which surely has occurred in some areas. I'd say the preponderance of evidence is for biological origin, but the evidence is not unambiguous.