GASCO Precision Calibration Gas 116es-428X-20 Mixture 20 PPM Hydrogen Sulfide, 1.45 % Methane,(29 % LEL,(58 % LEL Pentane Equivalent), 15% 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