Columbia subject headings:
Organization of Petroleum Exporting Countries--Statistics--Periodicals.
Petroleum industry and trade--Statistics--Periodicals.
Harvard subject headings:
Organization of Petroleum Exporting Countries--Statistics--Periodicals.
Petroleum industry and trade--Statistics--Periodicals
Princeton subject headings:
Organization of Petroleum Exporting Countries--Statistics--Periodicals.
Periodicals.
Petroleum industry and trade--Statistics--Periodicals.
Statistics.