The line graph illustrates the production levels of three types of fuels—coal, petroleum, and natural gas—over the period from 1981 to 2000, measured in energy units.
Petroleum consistently recorded the highest production levels throughout the period, peaking at 140 energy units in both 1986 and 1996. Natural gas production showed a steady increase, reaching its highest level of 100 energy units between 1996 and 2000. In contrast, coal, which began the period with a significant output of 80 energy units in 1981, demonstrated minimal growth and ultimately fell behind the other two energy sources by the end of the period.
In detail, petroleum production surged dramatically in the early years, climbing from 100 energy units in 1981 to a peak of 140 energy units in 1986, before stabilizing at that level in 1996. Similarly, natural gas production experienced a consistent upward trend, doubling from 50 energy units in 1981 to 100 energy units by the late 1990s. Meanwhile, coal, despite its strong start at 80 energy units in 1981, only saw a slight increase, ending at 60 energy units in 2000—40 units lower than natural gas during the same year.
Overall while both petroleum and natural gas showed significant growth, coal production stagnated, ultimately trailing behind its counterparts by the ending years.