Energy Supply and Energy Demand

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Throughout history, humans have depended on energy to meet their needs for cooking, heating, transportation, and other daily activities. The primitive man depended on energy in the form of food for his survival.

Table 1. Daily Per Capita Consumption of Energy (x1000 kcal)
Primitive man
1,000,000 years ago
Hunting man
100,000 years ago
Early agricultural man
5,000 years ago
Advanced agricultural man
1,000 years ago
Industrial man
100 years ago
Modern technological man
Transportation 1 14 63
Machinery* 4 7 24 91
Heating 2 4 12 32 66
Food** 2 3 4 6 7 10
Total 2 5 12 26 77 230
* Agricultural and industrial
** Including animal feeds
Source: Cook, E., “The Flow of Energy in an Industrial Society,
” Scientific American, p. 135, 1971.

The hunting man depended on energy 2.5 times more than the primitive man, as he learned to burn wood for cooking and heating. The demand increased even more when early human used animals to harvest crops. As agricultural society became more developed, wind and wave energies were harnessed to complement animal power to provide energy needed for farming and for transportation. The industrial revolution brought about by invention of the steam engine required increasingly more energy, mainly coal (See Table 1). By mid twentieth century, as society became more technological, and as demand for energy grew, coal was supplemented by petroleum, natural gas, and nuclear fuel. As Figures 1 and 2 indicate, the demand for energy has increased dramatically in the last few decades and is expected to continue to increase for the next few decades.

Because of various economical and technological factors, most of the energy used today is from non-renewable sources – mainly fossil fuels. Excluding hydroelectric, renewable energy has been almost completely ignored and constitutes around 1-2% of the total energy production.(1)

 World Energy Consumption, 1990-2030
Figure 1: World Energy Consumption, 1990-2030
 Historical and projected trends in energy demand between 1990-2030
Figure 2: Historical and projected trends in energy demand between 1990-2030


Energy Use in the United States

Currently, energy consumption in the United States is one of the highest in the world and is expected to remain so in the foreseeable future.( a ) The US, however, has long passed its peak oil production, and the reduction in petroleum had to be offset with other fuels, mainly coal and natural gas, or by foreign imports. (2) What is clearly evident is that energy resources are continuing to dwindle as both population and per capita consumption increase.

Table 2. Total U.S. Energy Consumption by Source, 2003
Energy Source Total Energy (Quad) Percent of Total
Petroleum 38.2 39.0
Natural Gas 23.5 24.0
Coal 22.5 23.0
Nuclear 7.8 8.0
Hydro 2.7 2.7
All others 3.3 3.3
Total 98 100

Question: At the current rate of consumption, every American uses energy at about twice the rate of Japanese or Europeans, and compared to Indians, the per capita consumption is 28 times greater. What contributes to the Americans’ higher rate of energy use? Answer: The large discrepancy is not only due to the large economies of the United States (and Canada), but is also a reflection of North Americans’ appetite for large cars, luxury items, and personal comfort.

Primary energy consumption in the United States by sources is given in Table 2 and Figure 5. About 86% of all energy used in the United States is from fossil fuels. All forms of renewable energy (biomass, hydroelectric, solar, wind, etc) make up 6% of energy needs. Because of its portability, convenience of use, and relatively greater energy density, oil is the fuel of choice for a variety of applications. The United States, as the biggest consumer of energy, uses one quarter of the total 85 million barrels per day of petroleum produced around the world. Petroleum consumption is limited mainly to transportation (Figure 4) and certain industrial processes (primarily petrochemical). Figure 6 gives the US total energy consumption by sectors. Each of the transportation, industrial processes, and residential and commercial sectors consume roughly a third of all energy. The pattern of energy use described here is not limited to the US alone; similar trends are observed in other regions of the world.

Energy Use in Other Parts of the World

Table 3. Energy Consumption for selected
Countries (Quads)
Country 1984 1994 2004  % rise
per year
Canada 9.8 12.0 13.6 1.6
United States 76.8 89.3 100.4 1.3
England 8.4 9.5 10.0 1.0
Japan 15.7 20.2 22.6 1.8
Russia NA 29.3 30.0 0.2
China 20.5 34.0 59.6 5.3
India 5.5 10.0 4 5.2
Iran 2.2 3.7 4 5.3
World Total 299.9 357.3 446.4 2.0

The recent data on energy consumption suggests moderate to rapid increases in the rates of fossil fuel consumption for various countries (Table 3). Russia’s growth was small due to instability following the breakup of the Soviet Union. US, Canada, and other industrial countries have had moderate growths in the past 20 years, whereas energy use in many developing countries increased significantly. For example, for the same 20 year period, the energy consumptions in China and India were tripled. The rapid increase is explained by a relatively faster rate of population growth and a higher per capita consumption reflected in higher total industrial outputs of these countries.

It is expected that in a near future, many under-developed countries will demand a greater portion of the world’s petroleum resources. The increase will be higher in developing countries that aggressively push for industrialization and more rapid economical growth. In light of the fact that some of these countries (notably Iran) are themselves, oil producing, a higher fraction of their output goes for domestic consumption, leaving less to import.

 US petroleum consumption by sector.
Figure 4: US petroleum consumption by sector.
 US total energy use by source.
Figure 5: US total energy use by source.
 US total energy use by sector
Figure 6: US total energy use by sector

Energy Reserves

It is very difficult to predict the total amount of energy reserves in the world, as by definition, renewable energy sources will be infinite. What is certain is that we will sooner or later run out of nonrenewable resources, primarily fossil fuels. The time that it will take to use up the remaining fossil resources is closely related to the accuracy of estimates of proven energy reserves and the rate at which new resources are found and extracted. The rate of consumption of fossil fuels is equally hard to predict, as it is affected by numerous factors such as population growth, economic activity, cost, environmental concerns, and the availability of other resources. Many studies suggest that within the next 30 to 50 years, we will have depleted most, if not all, of the natural gas and oil in the world. Even coal has a limited life and cannot be the answer to our long-term energy needs.


(1) US DoE, Energy Information Administration, Monthly Energy Review, July 2003.

(2) “Annual Energy Outlook with projection to 2025,” Energy Information Administration website (

(3) Toossi Reza, "Energy and the Environment:Sources, technologies, and impacts", Verve Publishers, 2005

Additional Comments

(a) As we shall see later, energy cannot be consumed, only transformed from one form to another.

Further Reading

Meadows, D. H., et al., The Limit to Growth, Universe Books, 1972. Also see, The Limit to Growth: The 30-Year Update, Chelsea Green Publishing Company, 2004.

Diamond, J., Collapse: How Societies Choose to Fail or Succeed, Penguin Group, USA, 2004.

Cleveland, C. J., Encyclopedia of Energy, Elsevier Direct Science, 2004.

The International Journal of Energy, Science Direct Elsevier Publishing Company.

Applied Energy, Elsevier Publishing Company.

Journal of Energy Resource Technology, ASME International.

The Energy Journal, The quarterly journal of the IAEE’s Energy Education Foundation, (

External Links

Energy Citation Database, US Department of Energy (

Environmental Protection Agency (

US Department of Energy (

The NIST Reference on Constants, Units, and Uncertainty (

The Club of Rome (

The Sierra Club (