Carbon Monoxide to be more specific. We purchased a carbon monoxide compressor. We can inject Carbon Monoxide into the ground at 120 psi per injector at 4 different injection locations. The compressor will fill a 200 foot long mole tunnel with Carbon Monoxide in seconds. Any mole or vole in those tunnels will die within seconds. The gas will travel a couple hundred feet into any tunnels in the surrounding area that is connected to the tunnels in your lawn.