Columbia subject headings:
Atmospheric methane.
Coal mines and mining--Environmental aspects.
Coalbed methane--Recycling.
Harvard subject headings:
Atmospheric methane.
Coal mines and mining--Environmental aspects
Coal--Environmental aspects
Coalbed methane--Recycling.
Methane--Environmental aspects.
Princeton subject headings:
Atmospheric methane.
Coal mines and mining--Environmental aspects.
Coalbed methane--Recycling.