Columbia subject headings:
Casebooks (Law)
Natural gas--Cases.
Natural gas--Law and legislation.
Natural gas--United States.
Petroleum industry and trade--Cases.
Petroleum industry and trade--United States.
Petroleum law and legislation.
Harvard subject headings:
Natural gas--Cases.
Natural gas--Law and legislation
Natural gas--United States
Petroleum industry and trade--Cases.
Petroleum industry and trade--United States
Petroleum law and legislation.
Princeton subject headings: