Columbia subject headings:
Coal--United States.
Natural gas--United States.
Natural resources.
Petroleum--United States.
United States--Economic conditions--1918-1945.
United States--Population.
Water-power--United States.
Harvard subject headings:
Coal--United States
Natural gas--United States
Natural resources
Petroleum--United States
United States--Economic conditions--1918-1945.
United States--Population.
Water-power--United States
Princeton subject headings:
Coal--United States.
Natural gas--United States.
Natural resources.
Petroleum--United States.
United States--Economic conditions--1918-1945.
United States--Population.
Water-power--United States.