Columbia subject headings:
Petroleum industry and trade--Vertical integration--United States.
Petroleum industry and trade--Vertical integration.
Trusts, Industrial.
Harvard subject headings:
Petroleum industry and trade--United States--Vertical integration.
Petroleum industry and trade--Vertical integration.
Trusts, Industrial.
Princeton subject headings:
Petroleum industry and trade--Vertical integration--United States.
Petroleum industry and trade--Vertical integration.
Trusts, Industrial.