Answer:

METHANE

Answer	Crossword Clue
METHANE	Marsh gas
METHANE	CH4
METHANE	Marsh hydrocarbon

METHANE	Swamp gas, essentially
METHANE	Swamp gas, mostly
METHANE	Marsh gas, mostly
METHANE	It's a gas
METHANE	Polluting gas
METHANE	Coal mine product
METHANE	A natural gas
METHANE	A greenhouse gas

METHANE	Hydrocarbon used as fuel.
METHANE	Marsh gas.
METHANE	Firedamp.
METHANE	Dangerous mine gas.
METHANE	It's a gas!
METHANE	Marsh gas, essentially
METHANE	Marsh gas constituent
METHANE	Natural gas constituent

METHANE	Dangerous buildup in a mine
METHANE	Coal miner's concern
METHANE	Greenhouse gas produced by cows
METHANE	CH4 (natural gas)
METHANE	Type of gas
METHANE	Flammable gas
METHANE	Fuel gas
METHANE	Marsh emanation

METHANE	Firedamp, for the most part
METHANE	Dairy farm product