Columbia subject headings:
Petroleum industry and trade--Government ownership--Mexico.
Petroleum industry and trade--Mexico--History.
Petroleum workers--Labor unions--Mexico--History.
Petroleum workers--Mexico--History.
Harvard subject headings:
Petroleum industry and trade--Government ownership--Mexico
Petroleum industry and trade--Mexico--History.
Petroleum workers--Labor unions--Mexico--History.
Petroleum workers--Mexico--History.
Princeton subject headings:
Mexico--Economic conditions--1918-
Petroleum industry and trade--Government ownership--Mexico--History.
Petroleum industry and trade--Mexico--History.
Petroleum workers--Labor unions--Mexico.