GASCO Calibration Gas 74-499BS Mixture 0.50 % Carbon Monoxide, 130 PPM Hydrogen Sulfide, 1.25 % Methane (25 % LEL), 11.78 % Oxygen, Balance Nitrogen Contained in a 74L Liter Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA