A single cell protein plant is operated to produce high density cell growth and a substantially pure stream of generally high pressure carbon dioxide for further use, for example, in enhanced oil recovery operations. The plant employs an air separator producing substantially pure streams of oxygen and nitrogen. The oxygen stream is used to enrich a carrier fluid and used for aeration of the fermenter. The off-gases from the fermenter are separated into a generally high pressure, substantially pure carbon dioxide stream which can be used for enhanced oil recovery and a residual recycle stream to which oxygen is again added and which is returned to the fermenter. The single cell protein is dried and further processed as required for human or animal consumption.