The two graphs show the main sources of energy in the USA in 1980 and 1990. Write a report for a university lecturer describing the changes which occurred.

The charts compare, in percentage terms, five fuel sources used to produce energy
in the USA in 1980 and 1990. Overall, oil was the main resource used for energy production in both years. There was relatively little change in the proportions of the other fuel sources used in 1980 and 1990. In 1980, 42% of energy produced in the USA came from oil, but this then fell to 33% in 1990. The figures for natural gas, in contrast, remained almost stable at 26% of total energy production in 1980 and 25% in 1990. There was, however, a significant increase in the proportion of coal used as an energy source. From a figure of 22% in 1980, it then overtook natural gas in 1990, with 27%. While the figure for hydroelectric power remained constant at 5% of the total in both years, the percentage of nuclear power used to produce energy rose by 5% from the 1980 figure, to reach 10% in 1990.