The given graph shows the main sources of energy for USA in 1980 and 1990.

The pie chart illustrates the changes in energy production from 5 different sources (oil, natural gas, coal, hydro-electric power and nuclear power) for the USA in two different years (1980 and 1990).

Overall, oil was the highest source of energy in both years while hydro-electric power was the lowest. The amount of energy produced by each source had changed inconsiderably over the decade. While oil and natural gas had declined, coal and nuclear power had increased their energy production.

The total energy generated by oil in USA, which had started out at 42% in 1980, had dropped to 33% by 1990. The ratio of hydro-electric power produced, on the other hand, was equal in both years at a mere 5%.

The energy generated by natural gas in USA accounted for 26% of the total energy in 1980, earning it the title, second highest in production. By 1990, it had declined by 1% to producing a quarter of the total energy. In contrast, coal and nuclear power had both snowballed in the volume of energy they yielded over the ten years, rising from 22% and 5% to 27% and 10% respectively by 1990.