Abstract: An air separation method and apparatus in which a compressed and purified air stream is divided into first and second subsidiary streams. The air of the first subsidiary stream is rectified within an air separation unit comprising higher and lower pressure columns. A liquid oxygen product is pumped from the lower pressure column to a desired above-atmospheric delivery pressure. At the same time, the second subsidiary stream is expanded to substantially the delivery pressure by an expansion machine and the two streams are then counter-currently added to a mixing column to vaporize the liquid stream and thereby produce a product stream at the delivery pressure. One or more liquid refrigerant streams are removed from the mixing column and added to the lower pressure column to refrigerate the process. The addition of a liquid increases the liquid to vapor ratio within the lower pressure column to in turn increase production.