Columbia subject headings:
Natural gas--Bibliography.
Natural gas--United States--Bibliography.
Petroleum industry and trade--Bibliography.
Petroleum industry and trade--United States--Bibliography.
Harvard subject headings:
Natural gas--Bibliography.
Natural gas--United States--Bibliography.
Petroleum industry and trade--Bibliography.
Petroleum industry and trade--United States--Bibliography.
Princeton subject headings:
Natural gas--Bibliography.
Natural gas--United States--Bibliography.
Petroleum industry and trade--Bibliography.
Petroleum industry and trade--United States--Bibliography.