GASCO 58L-425, Carbon Monoxide 35 PPM, Pentane 10% LEL, Hydrogen Sulfide 10 PPM, Oxygen 18%, Balance Nitrogen, Calibration Gas, contained in a 58L Liter Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA