Columbia subject headings:
Gas industry--Cost of operation--Statistics--Periodicals.
Natural gas reserves--Statistics--Periodicals.
Petroleum industry and trade--Cost of operation--Statistics--Periodicals.
Petroleum reserves--Statistics--Periodicals.
Harvard subject headings:
Gas industry--Cost of operation--Statistics--Periodicals.
Natural gas reserves--Statistics--Periodicals.
Petroleum industry and trade--Cost of operation--Statistics--Periodicals.
Petroleum reserves--Statistics--Periodicals.
Princeton subject headings: