Abstract: A method and apparatus for producing an oxygen product in which air is separated in an installation including one or more air separation units having higher and lower pressure columns. An exhaust stream produced from a turboexpander and optionally an impure oxygen stream such as that derivable from higher pressure column bottoms is rectified within an auxiliary column to produce an oxygen containing stream that is introduced into the lower pressure column of each of the air separation units to increase the capacity of such columns. The pressure within the auxiliary column is set by the pressure of the exhaust stream such that a nitrogen-rich vapor stream extracted from the top of the auxiliary column can be used in regenerating adsorbent within a pre-purification unit utilized in connection with the installation.