The present invention relates to a method and apparatus for producing a pressurized product stream product by cryogenic rectification. A main heat exchanger, used in the cryogenic rectification, warms a pumped product stream composed of oxygen-rich or nitrogen-rich liquid and thereby produces the pressurized product stream. Layers of the main heat exchanger are designed such that a reduction in the heat transfer area provided within the main heat exchanger for warming the pumped product stream occurs at a location at which the temperature of the pumped product stream exceeds either the critical or a dew point temperature of such stream. The reduction in heat transfer area leaves regions of the layers able to heat or cool another stream that is used in connection with the cryogenic rectification. Such other stream can be a refrigerant stream that allows the introduction of additional refrigeration to increase production of liquid products.