GASCO Calibration Gas 116es-409-ISO Mixture 50 PPM Carbon Monoxide, 25 PPM Hydrogen Sulfide, 100 PPM Isobutylene, 2.5 % Methane (50 % LEL), 12 % Oxygen, Balance Nitrogen Contained in a 116 Liter Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA