This publication covers the selection of gas cylinders: seamless steel cylinders, seamless steel tubes, welded steel cylinders, and nonrefillable steel cylinders used for carbon monoxide and for carbon monoxide/ carbon dioxide mixtures, e.g., laser gases. Intentionally made mixtures containing less than 5 parts per million by volume (ppmv) carbon monoxide or 5 ppmv carbon dioxide are not affected by this publication.