Columbia subject headings:
Harvard subject headings:
Natural gas reserves--Colorado.
Natural gas reserves--Nebraska.
Natural gas reserves--Wyoming.
Natural gas--Colorado.
Natural gas--Nebraska.
Natural gas--Wyoming
Oil fields--Colorado.
Oil fields--Nebraska.
Oil fields--Wyoming.
Princeton subject headings:
Natural gas--Colorado--Reserves.
Natural gas--Nebraska--Reserves.
Oil fields--Colorado.
Oil fields--Kansas.
Oil fields--Nebraska.
Oil fields--Wyoming.
Petroleum--Colorado--Reserves.
Petroleum--Nebraska--Reserves.