GASCO Calibration Gas 650es-411x-10SO2-20.9 Mixture Oxygen 20.9%, SO2 10 PPM, H2S 25 PPM, 25% LEL Pentane, Balance Nitrogen Contained in a 650 Liter Factory refillable cylinder, For Use with Any and All Gas Detectors, Cylinder Connection CGA TBD, Calibration Certificate NIST, Made in the USA