Columbia subject headings:
Canada--Foreign economic relations--United States.
Natural resources--Canada.
Natural resources--United States.
United States--Foreign economic relations--Canada.
Harvard subject headings:
Canada--Foreign economic relations--United States.
Natural resources--Canada.
Natural resources--United States
United States--Foreign economic relations--Canada.
Princeton subject headings:
Canada--Foreign economic relations--United States.
Canada. Natural Resources Canada.
Natural resources--United States.
United States--Foreign economic relations--Canada.