GASCO Calibration Gas 900es-421-15CO2-2% Mixture Carbon Monoxide 100 PPM, Carbon Dioxide 2% Volume, Hydrogen Sulfide 15 PPM, Methane 2.5% (50% LEL), Oxygen 18%, Balance Nitrogen Contained in a 900 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection CGA TBD, Calibration Certificate NIST, Made in the USA