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3.1: Fossil Fuel Resources

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    There are three major types of fossil fuels:

    • Those derived from naturally occurring petroleum forms, which include liquid oil, tar sands, and oil shales – by refining them, one obtains gasoline, diesel fuel, and aviation fuel (kerosene).Petroleum. Here, we will use the term crude oil for all the mined forms, and a general term of oil-products for all of the refined forms.
    • Natural gas, which is essentially methane CH4 with small admixtures of other gasses.
    • Coal – all its types.

    A unit measure used for oil and its liquid derivatives is a barrel (37.5 US gallons, or 119.24 liters). Because oil is now the “king” of fossil fuels, it has become a custom to express the amount of the other two fuels in units called Barrel of Oil Equivalent BOE. A BOE of coal is the amount of coal that releases, when burned, the same amount of energy as burning a barrel of oil (6.1 GJ)– it’s 200 kg, or 0.2 ton of coal. For natural gas at normal pressure, one BOE is 5,800 cubic feet, or 164.23 cubic meters (the US Geological Service uses 6,000 cubic feet, or 170 cubic meters).

    Comprehensive data concerning the resources and the consumption of fossil fuels can be found in several different Web documents – we recommend the Fossil Fuels site, a section of a larger Web document maintained by the Our World in Data, a project produced by the Oxford Martin Programme on Global Development at the University of Oxford, U.K., and is made available in its entirety as a public good.


    The global resources of recoverable oil (including liquid oil, tar sands, and shale oil) are estimated to be as high as about 1,700 billion barrels. The three countries possessing the largest oil deposits are Venezuela, Saudi Arabia, and Canada (with 300, 266.6, and 172,2 billion barrels, respectively). The US resources are estimated to be about 55 billion barrels.

    The estimated global resources of natural gas are 187 trillion cubic meters, equivalent to 1,139 billion BOE.

    The estimated coal resources, including all forms, from the high-quality (anthracite) to the lowest-quality lignite (also known as “brown coal”) are 1.1 trillion tons, or 5,500 billion BOE.


    The data concerning various aspects of fossil fuels are often given in different units (which may be a nightmare for the reader, and even for an author of a text like this one). It’s easier to find annual production than annual consumption data – not a big problem, because most of the oil mined is promptly refined and consumed, so that one can safely assume that the production and consumption data are equal. But to make things worse, the production data in the Internet source quoted above are given in TWh, while we would prefer BOE data. Fortunately, on the Web, using Google or another search engine, one can find right away programs converting one kind of units to another kind. So, one such program informs us that:

    1 TWh = 588,235 BOE

    Fine! So, let’s begin with oil. In the Fossil Fuels site we read from a chart that in 2016 the annual production of crude was 51,000 TWh – and by multiplying this number by the above conversion factor, we obtain almost exactly 30 billion barrels. Now, we take the global resources, 1,700 barrels – and we get that if oil is mined from now on at the same level as in 2016, the resources will be all gone about 57 years from now.

    For the author of this text, who was born the at the same year as the WW II ended, for obvious reasons it’s not a threatening perspective – but if you, Dear Reader, are an undergraduate student, it may be a piece of bad news!

    Let’s then look at natural gas. Again, the storage of natural gas is difficult (it may be stored in in a liquefied form, which is the called LNG, but it’s being done mostly for transporting the gas, not for storing it for a long period (a much better method of long-time storage is to keep the gas underground!). So, here we can again assume that the annual consumption and the annual production are equal. In the Fossil Fuels site we find that the annual production is 37,366 TWH, which converts to 21.98 billion BOE. By dividing the known reserves, 1,139 billion BOE, by the latter number, we obtain a period of about 51.8 years. Again, not very good news!

    The last one on our list is coal. Since there is a serious danger that all oil and gas resources will be gone before the end of this century, perhaps coal is the “last resource” for future generations? Well, there are no reasons for too much optimism. In 2016, the production of all coal types was about 42,500 TWh, equivalent of 25.0 billion of BOE. Considering that the global resources are 5,500 billion BOE, we get 220 years. Do we? Not really! Because when all oil and natural gas resources are exhausted, coal must substitute for the two other missing fuels! It must be used in much higher annual rate, if we still want to generate as much power from fossil fuels as we did when oil and gas were still available!

    Making estimates of how long the coal resources will last if coal indeed will be used to “fill the gap” left by exhausted oil and gas deposits is difficult – let’s not try to do that here, but let’s rather check what professionals claim. The problem is discussed, for instance, in this Web document. From the graph presented in this site, one can see that the authors of the document don’t even expect the coal resources to last beyond the end of this century! There is always some room for optimism, because new deposits of fossil fuels are still being discovered. For instance, the recoverable oil reserves in the United States in 2005 were estimated as 29.9 billion barrels, and ten years later, in 2015, as 50 billion barrels. Such a big change was due to two factors: new oil fields in North Dakota, and the invention of a new “fracking” technology that allows to pump more oil from deposits that were considered fully emptied. Similarly, the estimates of natural gas resources, which were 1200 trillion cubic feet in 2002, increased to over 2,400 trillion cubic feet in 2013. Again, it was due to discovering new gas fields and to developing new technologies of horizontal drilling and fracking.

    On the other hand, people who are even strong enthusiasts of using fossil fuels should keep in mind that there are not mined with the sole purpose of burning them in power plants, smelters, heating furnaces, or gasoline, diesel, and jet engines. Oil and natural gas (and coal, to a lesser degree) are the basic raw material for many branches of chemical industry, making products of crucial importance for our lives: plastics, fertilizes, drugs, and dozens of others. If we keep burning fossil fuels as long as they are available, our lives may become miserable... And another important reason to start showing restraint in burning fossil fuels is that we are adding more and more CO2 to the atmosphere. The concentration of CO2 in the atmosphere is rapidly growing.

    The CO2 concentration in atmospheric air is monitored by many obser-

    vation posts around the globe – the best known of which is the one located at Hawaii, at the Mauna Loa volcano at the altitude of 4169 meters above the sea level. Hawaii archipelago is located in the middle of the Pacific Ocean, far away from any big industrial center that might be able to create a local increase above the average concentration. On the graph in Fig. 3.1, one can see a steep curve with characteristic saw-teeth-like oscillations. This is the so-called Keeilng Curve, in which the the saw-teeth-like features represent the seasonal variations of the carbon dioxide concentration. Why does it change with seasons? The answer is simple: in May, the concentration starts decreasing, which reflects the fact that the vegetation, grasses and trees, start growing new leaves, and they are rapidly absorbing CO2 from the air. The process lasts for several months, producing a “dip” on the curve, until the leaves fall and start rotting – now, in turn, releasing CO2 into the air.

    Well, one may have some doubts concerning such an explanation. The spring starts in May, yeas, but only at the northern hemisphere – and at the southern, it starts in 6 months later in the same calendar year, in November. So, the southern hemisphere vegetation should give rise to a similar “dip” phase-shifted by 6 month relative to that caused by the northern-hemisphere vegetation. Hence, the two effects should cancel each other!

    Figure \(\PageIndex{1}\): Atmospheric CO2 concentration at Mauna Loa Observatory (from Wikimedia.commons)

    Yes, it would be so, but the thing is that most landmass, and most vegetation on Earth is on the northern hemisphere. Especially, the boreal forests of northern Russia (the “taiga”) and of northern Canada are much stronger CO2 absorbers/emitters than anything that can be found in the southern hemisphere. For instance, the famous enormous rainforest in the basin of Amazon River is all evergreen, so that it does not contribute to the seasonal variation of CO2. Therefore, the southern hemisphere vegetation plays only a minor role in the process.

    However, if there were only seasonal variations, the Keeling Curve, when averaged, should be flat – but in fact, it’s rapidly growing. When the Author of this text for the first time learned about the CO2 concentration in the atmosphere, it was 0.03% = 300 ppm, and now, 60 years later, it has already exceeded 400 ppm.

    So what? – some people angrily ask. Where is the problem? Here we have come to one of the major controversies of our times. There is no doubt that the increasing concentration of CO2 is antropogenic, i.e., caused by the activity of us, humans. And in the scientific community, the majority of its members agree that the increasing concentration of CO2 is responsible for global warming. In 2015, a United Nations Framework Convention on Climate Change was held in Paris. There was a consensus among the 195 participating nations (summarized in the document worked out by the conference, the so-called Paris Agreement ) that keeping the CO2 emission at the current (or higher) rate will lead in the near future to a global temperature increase of 2C over the pre-industrial level, i.e., the average global temperature at 1880. The participants declared to voluntarily mitigate the emission of CO2 by their countries. It is not known exactly by how much the emission should be cut down to meet the goal – there is no well-established theory of how the CO2 concentration in the atmosphere is correlated with he global temperature. The data on which the Paris Agreement recommendations has been based are published in a 2013 Intergovernmental Panel on Climate Change. The Paris Agreement recommendations are often termed the carbon budget. In short, it says that if we want to achieve a 50% probability of limiting warming to 2, we have to leave the majority (up to 80 percent) of our fossil fuels in the ground (for more details, see the Unburn-able Carbon Section in the Fossil Fuels Web page. OK, if 80% of fossil fuels should stay in the ground – then, if they are mined at the current rate, they will “run out” much faster than we predicted above – or, the pace of mining them from the underground must be drastically reduced.

    On the other hand, there are many groups of people (including some scientists) who argue that man-made global warming is a “hoax”. They use different arguments, or no arguments – there make no sense to quote them here, because this would be off-topic. The main point in this Section is: “How long will the fuel resources last?” – so the answer to this question depends not on who is right (those who believe in man-made global warming, or global warming skeptics?), but which one of those two groups will win the dispute. And the skeptics have many supporters – beginning from very-high placed politicians, to big business leaders whose profits are correlated with the rate of fuel extraction, and – last but not least – to people who live from mining fuels, i.e., simple coal miners or operators of gas or oil wells. The combined influence of such people on public opinion may be quite strong, and may decide, for instance, on who wins the elections.

    So, it’s not possible to predict which group will take over. If the global warming skeptics, then mining of fossil fuels may last longer. Recently, the Trump Administration declared it would withdraw the United States form the Paris Agreement (it cannot happen immediately – the earliest possible effective withdrawal date by the United States cannot be before November 4, 2020, four years after the Agreement came into effect in the United States). It’s always possible that other countries may do the same. Regretfully, the only thing that one can do now is “to wait and see”.

    3.1: Fossil Fuel Resources is shared under a CC BY 1.3 license and was authored, remixed, and/or curated by Tom Giebultowicz.

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