Abstract: A compressed air stream is separated in a double rectification column having a higher pressure stage and a lower pressure stage. The lower pressure stage contains a low pressure drop liquid-vapor contact means having a pressure drop of less than about 400.0 Pa per theoretical stage, for example a structured packing, to effect mass transfer between ascending vapor and descending liquid. A product gaseous oxygen stream is withdrawn from the lower pressure stage through an outlet thereof and is warmed to about ambient temperature in a heat exchanger in countercurrent flow relationship with the compressed air stream which is thereby cooled. Refrigeration for the process is created by expansion of part of the incoming air.