Columbia subject headings:
Gas industry--Caspian Sea Region--History.
Gas industry--Caucasus--History.
Petroleum industry and trade--Caspian Sea Region--History.
Petroleum industry and trade--Caucasus--History.
Harvard subject headings:
Gas industry--Caspian Sea Region--History.
Gas industry--Caucasus--History.
Petroleum industry and trade--Caspian Sea Region--History.
Petroleum industry and trade--Caucasus--History.
Princeton subject headings:
Petroleum industry and trade--Caspian Sea Region--History.
Petroleum industry and trade--Caucasus--History.