An oxygen production method and apparatus including an air separation plant and a heat exchanger in which a pumped liquid oxygen stream is heated within the heat exchanger through indirect heat exchange with compressed air to produce a pressurized oxygen product. The liquid oxygen stream is pressurized to above about 55 bar (a) and no greater than about 150 bar (a) and is a supercritical fluid after having been heated. The air is compressed to an air pressure that is a function of the oxygen pressure that will result in a minimum power being expended in the compression of the air. The heat exchanger can be a brazed fin heat exchanger fabricated from aluminum in which the fins located in heat exchange passages have an undulating configuration to increase the flow path length and induce flow separation and thereby increase the heat transfer coefficient within the heat exchanger.
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