Columbia subject headings:
Harvard subject headings:
Gas industry--Europe--Directories.
Gas industry--Europe--Periodicals.
Natural gas--Europe--Periodicals.
Petroleum industry and trade--Europe--Directories.
Petroleum industry and trade--Europe--Periodicals.
Princeton subject headings:
Gas industry--Europe--Directories.
Gas industry--Europe--Periodicals.
Natural gas--Europe--Periodicals.
Petroleum industry and trade--Europe--Directories.
Petroleum industry and trade--Europe--Periodicals.