GASCO Calibration Gas 650es-428-20SO2 60 PPM Carbon Monoxide, 20 PPM Hydrogen Sulfide, 5 PPM Sulfur Dioxide, 1.45% Methane (29% LEL), (58% LEL Pentane Equivalent), 15% Oxygen, Balance Nitrogenn 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