GASCO Precision Calibration Gas 34es-411-18CO2 Mixture 25% LEL Pentane, 18% Oxygen, 100 ppm Carbon Monoxide, 25 ppm Hydrogen Sulfide, 2.5% Carbon Dioxide, Balance Nitrogen Contained in a 34 Liter Factory Refillable ecosmart Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA