As we saw in Chapter 2, the population of the world rose nearly four-fold during the twentieth century, from 1.6 billion in 1900 to approximately 6.1 billion in 2000. However, world primary energy use increased at a much faster rate. Between 1900 and 2000, it rose more than 10-fold

For most human history the world's principal fuel was firewood (or other forms of traditional ‘bioenergy’), but by the beginning of the twentieth century coal use was rising fast replaced wood as the dominant energy source. During the 1920s, oil in turn began to challenge coal and by the 1970s had overtaken it as the leading contributor to world supplies. By then, natural gas was also making a very substantial contribution, with nuclear energy and hydro power also supplying smaller but significant amounts.

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On average, world primary energy use per person in 2000 was about 70 thousand million joules (70 gigajoules), including non-commercial bioenergy. This is equivalent to about one and two-thirds tonnes of oil per person per year, or about 5 litres (just over one Imperial gallon) of oil per day. But this average conceals major differences between the inhabitants of different regions.

North Americans annually consume the equivalent of about 8 tonnes of oil per head (about 20 litres per day), whereas residents of Europe and the former Soviet Union consume about half that amount, and the inhabitants of the rest of the world use only about one-tenth. World consumption per person has shown almost no growth over the past 20 years. North American consumption per capita is more than twice that of Europe and the former Soviet Union, and almost 10 times the level in the Rest of the World.

Per capita primary energy consumption, in tonnes of oil equivalent per year, for different regions of the world and for the world as a whole, 1975–2000

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