GASCO Precision Calibration Gas 650es-428X-20 Mixture 20 PPM Hydrogen Sulfide, 1.45 % Methane,(29 % LEL,(58 % LEL Pentane Equivalent), 15% Oxygen, 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