A: You probably have other hydrocarbons in your gas. The methane detector is sensitive to all hydrocarbons, so the presence of ethane, propane, butane and others in your gas stream will cause your methane reading to be too high. LANDTEC sells “Charcoal Absorber Filters (1-00000-5084)”, which will reduce the contamination from non-methane hydrocarbons. For more information, see section on “Cross Gas Effects” of the GEM™2000 Manual