GASCO 499 Calibration Gas Mixture 100 PPM Carbon Monoxide, 75 PPM Hydrogen Sulfide, 2.5 % Methane (50 % LEL) , 15 % Oxygen, Balance Nitrogen in a 650 Liter,For Use with Any and All Gas Detectors, Cylinder Connection: TBD Gas Specific, Calibration Certificate NIST, Made in the USA