Columbia subject headings:
Labor unions--Mexico--History.
Petroleum workers--Mexico--History.
S.T.P.R.M. (Organization)--History.
Harvard subject headings:
Petroleum workers--Labor unions--Mexico--Officials and employees--History--20th century.
Petróleos Mexicanos--History--20th century.
S.T.P.R.M. (Organization)--Officials and employees.
Princeton subject headings:
Petroleum workers--Labor unions--Mexico--History.
S.T.P.R.M. (Organization)--History.