Columbia subject headings:
Natural gas--Law and legislation--United States--States.
Natural gas--Law and legislation--United States.
Petroleum law and legislation--United States--States.
Petroleum law and legislation--United States.
Harvard subject headings:
Natural gas--Alberta.
Natural gas--Law and legislation--Alberta.
Natural gas--United States
Petroleum law and legislation--Alberta.
Petroleum law and legislation--United States--States.
Petroleum law and legislation--United States.
Petroleum--Alberta
Petroleum--United States
Princeton subject headings:
Natural gas--Alberta.
Natural gas--United States.
Petroleum--Alberta.
Petroleum--United States.