Columbia subject headings:
Harvard subject headings:
Natural gas--Environmental aspects--Congresses.
Natural gas--Industrial applications--Congresses.
Natural gas--Safety measures--Congresses.
Natural gas--Technological innovations--Congresses.
Princeton subject headings:
Natural gas--Environmental aspects--Congresses.
Natural gas--Industrial applications--Congresses.
Natural gas--Safety measures--Congresses.
Natural gas--Technological innovations--Congresses.