The total amount of oil that is still in the ground and that can be pumped out with current technology—known as proven oil reserves—is 1800 billion barrels.*  About 100 million barrels of oil is consumed daily.  And so, if no major new oil discoveries are made, if there is no major advance in the ability to extract oil and if worldwide consumption remains the same, then, by simple division, there are about 18,000 days (or about 50 years) until the amount of oil runs out.


New discoveries are made and oil-extraction technology does become more efficient, though the amount of oil is not infinite.  And consumption does change.  So how much oil remains?


Much of the world has already been explored for oil.  And most of the oil comes from a few major oil fields.  Of the thousands of oil fields that have been discovered, a third of the oil has come from the twenty-five largest fields—and, of those, all but two were discovered before 1970.  Moreover, whatever gains are to be realized by improvements in oil-extraction technology will be offset by increases in worldwide consumption.  The bottom line is this:  In the future, the total amount of oil as proven reserves will probably not increase much above the current amount.  There is enough oil left in the ground today to run the world economy for several more decades.  But there is a substantial amount of potential oil in the form of oil shale.


Oil shale is a misnomer:  It is neither composed of oil or of shale.  What looks like shale is actually limestone.  And what seems to be oil is an organic, waxy material known as kerogen.  


Kerogen is an early stage in the natural production of oil, but it has not been subjected to high enough pressure or high enough temperatures over a sufficient length of time to be converted into oil.  Oil can be made from kerogen, but the process is difficult and expensive and there is no economically viable way to do it today.


The amount of potential oil that could be made from kerogen is staggering.  The World Energy Council estimated that the total world resources of equivalent oil is 6000 billion barrels.**  To retrieve it requires the digging up of vast tracks of land in places such as Wyoming, Colorado and Utah.  It could, possibly, supply oil to the world’s economy through this century and into the next.


But there are consequences to the continued use of oil.  Vast amounts of land will have to be disturbed to mine oil shale.  To extract oil from oil-rich rocks, the injection of high-pressure fluids, by a process known as fracking, must become more widespread.  Since 2018 most of the oil produced in the United States—which is now the world’s leading producer of oil—is done by fracking.  And that process, through the chemicals that are injected, can contaminate groundwater.  Fracking also requires the use of large volumes of freshwater, which is in greater and greater demand.  And large volumes of waste water are produced, which are poured into large ponds that cover large areas.


And the continued use of oil has another consequence:  It continues to inject large amounts of carbon dioxide into the atmosphere which is the main factor in the global rise of temperature of the atmosphere and of the oceans.



* For comparison, so far, 1300 billion barrels of oil have been produced around the world.

** Of that, nearly half is in the western United States in a series of rocks known as the Green River Formation.