The graph illustrates the energy units produced from three significant energy sources including coal, petroleum, and natural gas over the years.
Overall, the production of natural gas has seen a gradual increase over the years while the energy levels obtained from coal declined, particularly after 1991. Meanwhile, there is roughly a periodic fluctuation in manufacturing of petroleum over the decades.
The natural gas production levels remained constant for a decade between 1981 to 1991 with only 40 units of energy extracted from a million tonnes of oil. After 1991, the level steadily increased to reach 100 energy units of gas obtained by the year 2000, surpassing the coal production levels. Coal industry experienced a steep decline with units dropping from 80 to about 40 after 1983. However, it was until 1991, that the energy from coals kept decreasing and became the lowest energy producing source by 2000.
On the other hand, petroleum maintained its status as the highest energy producing source despite a brief decline in its production between 1986 to 1991. The energy production from petroleum remained between the range of 90 to 140 units of energy between 1981 and 2000.
