Also called Compound O, it is used following the tumbling of steel tanks to prevent flash rust, a reddish film which often forms on the interior walls during drying of the cleaned cylinder. This chemical replaces Compound B, a popular anti-rust agent which is NOT oxygen compatible. Compound O can be used for both air and O2 / Nitrox tanks. QUART. * No longer available after remaining inventory sold: Now only sold in Gallons (42220OX) or Pints (42224OX).