Oil Resources and Reserves

From R.L.McConnell & Daniel C. Abel, Environmental Issues. Measuring, Analyzing and Evaluating


The first successful oil well was drilled in the mid-19th century. However, oil consumption was insignificant for the next 50 or so years until Henry Ford began mass production of automobiles. Between 1919 and 1949 oil gradually replaced coal as the most important fuel source in the U.S. Presently, oil provides about half of the energy requirement of the U.S. and almost all of our transportation fuel.

According to 1996 statistics, nearly 72 million barrels (1 barrel = 42 gal) were consumed per day globally, with the U.S. consuming about a quarter of this amount (~18 million barrels).

Origin and Distribution

Oil is a non-renewable resource. Oil fields resulted from the burial of organic remains under sediments where decomposition occurred anaerobically under conditions of high temperature and pressure. For extraction and use, oil must migrate from it's original location far below the surface (source bed) into a geological structure capable of trapping and preventing it's escape. Ocassionally, pressure forces the oil to the surface where it forms seeps. The 19th century oil discoveries came about when wildcatters drilled holes into the rocks underlying seeps.

After extraction, oil is processed to remove other fluids such as salt water and then refined. During the refining process, the oil is heated in the absence of oxygen to break or "crack" the molecules into the smaller molecules we find in gasoline, diesel fuel, etc. The oil is then shipped to distinations around the world via pipeline or oil tanker.

Remaining Reserves

Calculation of the minimum amount of oil present in all of the earth's known oil fields and the amount that can be extracted utilizing current technology yields a value termed the world proven oil reserves. This value is usually an underestimation because companies often underestimate the amount of oil present in their fields. For example, BP (British Petroleum), in 1970, estimated that it's Forties North Sea oil field contained about 1.8 billion barrels of proven reserves. By 1995, BP had extracted 3.6 billion barrels and estimated that 2.8 billion barrels remained. Proven reserves are probably about half of the ultimately recoverable oil reserves (the total resource that can be extracted).

How Long Will It Last?
According to the World Resources Institute, world proven oil reserves were estimated at 1000 billion barrels in 1995. Since proven reserves are usually less than half the ultimately recoverable reserves, we will assume that about 2000 billion barrels of oil will be able to be recovered and used.

How long will the proven reserves last at our present rate of production (25.32 billion barrels per year)? If your starting point was 1997, when will the oil run out? (Assume that reserves were approximately the same in 1997 as 1995).

Unfortunately, the number that we just calculated is irrelevant because the rate of oil consumption is increasing.

World Oil Demand
YearConsumption (million barrels per day)
199773.700 (projected in part)
From Energy Information Administration.International oil data for crude oil production

Since the rate of oil consumption is increasing, we need to readjust our estimate for how long our oil reserves will last.

What is the percentage increase from 1986 to 97?

What was the average annual growth rate in oil consumption for the period 1986-97?
HINT: The average rate of increase is the value k in the formula t = (1/k)ln (N/N0).

It is important to note how a seemingly small rate of increase can lead to such a big change in oil consumption over a long period of time. The concept of doubling time can be applied to illustrate growth of consumption.

What is the doubling time for the increase in oil consumption you calculated above?

In 44 years, at an increase of 1.6% per year, the world would be consuming oil at a rate of 50.6 billion barrels annually by the year 2041.

Approximate the total amount of oil that would be consumed during this 44 year period.

How does this compare to the current estimate of total oil reserves?

Shale oil is often suggested as a viable substitute for oil. Shale oil resources (the total oil in shale, not that which can be economically extracted) in Wyoming, Utah, and Colorado have been estimated to exceed 2000 billion barrels - twice the world's proven oil reserves! Research the geology of oil shale and the limitations to mining oil shale. Consider the following:
  • water needs and availability
  • waste disposal
  • methods proposed for extracting the waxy, almost solid oil from the dense shale rock
  • energy required to extract the oil from the shale
Do you believe that shale oil is a viable replacement for oil in conventional rock reservoirs?