GASCO Calibration Gas 650es-499BS Mixture 0.50 % Carbon Monoxide, 130 PPM Hydrogen Sulfide, 1.25 % Methane (25 % LEL), 11.78 % Oxygen, Balance Nitrogen Contained in a 650 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection CGA 330, Calibration Certificate NIST, Made in the USA