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Abiotic Oil Formation

Though the current accepted theory of oil formation involves the slow transformation of animal and plant matter into hydrocarbon (the biotic or biogenic theory), it is not the only theory that has been put forth. As early as the 16th century, one theory of the origin of oil claimed that it resulted from deep carbon deposits that have been around far longer than life on this planet. The theory, which came to be known as the abiotic oil formation (AOF) theory, was largely forgotten until rather recently when a few people (some of them scientists) revived it.

The newest version of the AOF theory states that oil arises from inorganic processes that occur deep within the core or lower mantle of the Earth. Here, they say, oil is formed and then percolates up through cracks and porous rock to fill the reservoirs that humans tap to get oil. If this claim is true, then oil may not be nearly as limited in quantity as proponents of the biotic theory claim. This would mean oil is more “renewable” than we have been led to believe.


The AOF theory has been championed for a number of reasons, but many current proponents point to the presence of methane on comets, meteors, and other lifeless planets as evidence that organic material is not needed to produce petroleum. Other supporters point to other clues about the origins of oil such as the distribution of metals in oil, the association of hydrocarbons with helium, and the presence of oil deposits in large-scale structures rather than patchy sedimentary deposits. These, proponents claim, are all reasons to believe that oil does not come from plant and animal matter, but rather from some natural chemical process involving inorganic materials.

The theory persists for a number of reasons, but one of the biggest is that no one has actually ever witnessed the formation of oil. Because it takes millions of years for a fossil fuel to form, any theories we have about the process of formation is based on observations of current material. It is possible to speculate, make predictions and test those predictions to gain evidence to support or reject a given theory, but it is not possible to be as certain about the formation of oil as we are about something like the formation ice, which we can directly observe. So, which theory has more supporting evidence?


Most scientists believe the evidence comes down decidedly on the side of oil forming from deceased organic matter. They point to very strong chemical evidence (so called “biomarkers”) that show hydrocarbons have an organic origin and not an inorganic origin. They also point out that various stages of hydrocarbon development have been uncovered, showing the progression from say peat all the way to anthracite coal or from algae to oil. They also argue that small quantities of hydrocarbon can be produced in laboratories, thus strong supporting their stance.

Proponents of the abiotic theory are not without their evidence, however. These scientists point to the fact that oil reservoirs have been shown to refill when left alone for periods of time, something that does not fit with the biotic theory. They also point to the presence of oil on meteors and other bodies that do not and never have supported life. They also suggest that claims about the chemical nature of oil are spurious because we do not know what processes occur deep in the Earth that may cause oil to look as though it came from an organic source when it did not. It is also true that oil can be produced from inorganic material, lending support to this theory.


Most scientists support the biotic theory of oil production for a number of reasons. In response to the evidence for the abiotic theory, they say the following.

First, refilling of wells can be explained by two phenomena. One, our ability to extract oil from more difficult environments is constantly increasing. As a result, wells that were once “tapped out” can now be reopened and produce again using new technology. Two, because oil moves and is of different densities, it is true that pumping oil from a well may relieve pressure, which then allows oil trapped in cracks, faults, and other pockets to enter the well over time.

The second reason many scientists doubt the abiotic theory is that its basic tenets don’t seem to be viable. Namely, the idea that rocks at great depth are porous is the opposite of what research shows. Of course, proponents of the theory point to the fact that magma manages to escape, so why not petroleum.

The third and most substantial reason for discounting the abiotic theory is that the chemistry doesn’t add up. First, there doesn’t seem to be enough CO2 below the surface of the Earth to make the formation of oil possible. In scientific terms, the mass balance of the equation is errant. More importantly, however, is the distinct isotopic and biochemical structure of oil, which strongly support and organic origin. For example, helium that is trapped with hydrocarbon deposits (and is an inert gas so it does not react with anything), is of a specific character that means it almost certainly came from the surface of the Earth and not anywhere else.

What is clear is that these issues require more research and, given the importance of oil to our energy needs, many prestigious institutions are working to solve the dilemma. In the United States, scientists from the Woods Hole Oceanographic Institute are attempting to determine just how deep oil deposits can be found. The deeper they are, the less likely it is that they came from biotic origin.

The other possibility here is the both groups are right. Oil may form through both processes. If so, then oil may not be as limited a resource as we currently surmise.


Like many issues, politics play a major role in the abiotic versus biotic oil formation argument. Until recent decades, the main argument propelling each was the supposedly limited supply of fossil fuel available. For those pumping it from the ground, limiting supply has financial gain. For politicians, a limited supply can be used to control people and as justification for actions like war. An unlimited supply, on the other hand, means that we need not worry about running out, that we ought to be able to drill for more oil and increase the daily supply so as to decrease price, and so forth.

The arguments above, however, have been pushed aside in recent years by fears that global warming is directly attributable to carbon dioxide produced by burning hydrocarbons. If this is true, it doesn’t matter if oil is limited or not because using it is causing immense damage.

In the end, science will settle the debate, but what science gets funded is directly related to which politicians are in power and who is footing the bill. At some point we will know the definitive answers to questions about the origin of oil and to questions about the impact of CO2 on the environment.