Columbia subject headings:
Economic history--20th century--Congresses.
Petroleum industry and trade--History--20th century--Congresses.
Harvard subject headings:
Economic history--20th century--Congresses.
Petroleum industry and trade--History--20th century--Congresses.
Princeton subject headings:
Economic history--20th century--Congresses.
Petroleum industry and trade--History--20th century--Congresses.