Oil (and other carbon based fuels like Coal, but for this question, I'm more interested in Oil) is widely regarded as a "Fossil Fuel" because its origin was ancient flora and fauna, buried deep below the surface for millions of years while being transformed into oil.

Is this really the case?

Was there enough ancient plant and animal life trapped beneath the surface to account for known oil reserves?

People often say they are "filling their tank with dinosaurs" -- how much oil actually comes from dinosaurs or other animals versus other sources? A commenter asked for references for this claim, I thought the dinosaur gas tank connection was well known, here are a few references to dinosaurs in the gas tank:

How did this ancient life come to be buried thousands of feet below the current surface of the earth and oceans? Continental drift and other plate tectonics shifting?

Was this transformation process 100% complete? Are there any cases where ancient plant matter, fossils, etc were pumped to the surface from an oil well?

  • oil comes from plankton sinking and getting trapped beneath rock before fermenting Apr 23, 2013 at 19:44
  • semi related: skeptics.stackexchange.com/q/1050/6876
    – Ryathal
    Apr 23, 2013 at 20:37
  • You might, slightly more accurately, describe it as coming from the plants that fed dinosaurs .But even that is pinning down the timescale too tightly to be accurate for a geologist who cared about his precise terminology.
    – matt_black
    Apr 23, 2013 at 22:04
  • 1
    People often say they are "filling their tank with dinosaurs": please link to some relevant claim of someone saying that.
    – nico
    Apr 24, 2013 at 15:25

1 Answer 1


Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms including phytoplankton and zooplankton that settled to the sea (or lake) bottom in large quantities under anoxic conditions. (Giant Oil and Gas Fields of the Decade, 1990–1999, Tulsa, Okla.: American Association of Petroleum Geologists, p.50) The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years.

Over geological time, this organic matter, mixed with mud, got buried under heavy layers of sediment. The resulting high levels of heat and pressure caused the organic matter to chemically alter, first into a waxy material known as kerogen which is found in oil shales, and then with more heat into liquid and gaseous hydrocarbons in a process known as catagenesis. -source

I would not expect plant material to be found included in the oil. The organic material is compressed into kerogen during the formation process... oil is formed from that material (which is, in turn, imbeded in rock). As it turns into oil, it slowly seeps out of the source rock. The oil migrates until it is trapped in a reservoir rock layer (usually sandstone) that has an impenetrable seal layer (usually shale) above it.

Whether this constitutes "dinosaurs" depends on your definition. If you are discussing therapods, sauropods, and the various reptiles collectively referred to as "dinosaurs" in common culture then, with some statistically insignifigant exceptions, "no".

  • 4
    Welcome to Skeptics Stack Exchange! Please provide some references to support your claims.
    – Sklivvz
    Apr 23, 2013 at 21:34
  • @Sklivvz: The second link in your comment is broken.
    – user13526
    Apr 24, 2013 at 1:16
  • But the question is... do those organisms include dinosaurs? Sea dinosaurs perhaps?
    – Muz
    Apr 24, 2013 at 3:47
  • @EvanTeitelman fixed
    – Sklivvz
    Apr 24, 2013 at 8:55
  • Edited to add refreneces (one link, one book), and answer the question. Though ocean going dinosaurs may be included in oil, they are a vast minority of biomass so statistically "no".
    – JerryLove
    Apr 24, 2013 at 13:37

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