GASCO Calibration Gas 44es-417-18 50 PPM Carbon Monoxide, 25 PPM Hydrogen Sulfide, 0.7% Pentane (50% LEL), 18% Oxygen, Balance Nitrogenn Contained in a 44L Liter ecosmart Factory Refillable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA