GASCO Precision Calibration Gas 650es-429ST Mixture 25% LEL Methane, 15% Oxygen, 200 ppm Carbon Monoxide, 75 ppm Hydrogen Sulfide, Balance Nitrogen Contained in a 650 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection CGA TBD, Calibration Certificate NIST, Made in the USA