Columbia subject headings:
Mexico--Commerce--United States.
Petroleum industry and trade--Mexico.
United States--Commerce--Mexico.
Harvard subject headings:
Mexico--Foreign relations--United States.
Petroleum industry and trade--Political aspects--Mexico.
Petroleum industry and trade--Political aspects--United States
United States--Foreign relations--Mexico.
Princeton subject headings:
Mexico--Commerce--United States.
Petroleum industry and trade--Mexico.
United States--Commerce--Mexico.