The two charts show the main sources of energy in the USA in 1980 and 1990.Summarize the information by selecting and reporting the main features, and make comparisions where relevant.

The pie charts provide some information on the main resources of energy in the United States in the 1980 and 1990.

As can be seen from the chart, in 1980, oil, which was 42 percent, is the dominant source of energy. Then next is natural gas, with about 26 percent, followed by coal, making up 26 percent of all the main energy resources. Finally come nuclear power and hydroelectric power, both at 5 percent.

According to the second pie chart, the most common energy resource remained to be oil, accounted for 33 percent. Less coal (27%) and natural gas (25%) were consumed in 1990. A minority of energy resources was from nuclear power and hydroelectric power, only occupied 10 percent and 5 percent respectively.

Overall, from 1980 to 1990, United States witnessed a huge decrease in the proportion of oil and natural gas in the main sources of energy. On the contrary, the consumption of hydroelectric power was leveling off. Despite these significant changes, oil stayed the largest proportion of all the energy resources whereas usage of hydroelectric power remained to be the lowest.