Abstract: A method of boiling a liquefied gas in a heat exchanger 10 includes the step of introducing a seed gas via a pipeline 18 to spray nozzles 34 situated under passages 22 of the heat exchanger 10 for reboiling the liquefied gas, e.g. oxygen. The passages 22 alternate with passages 24 for condensing nitrogen vapor. The seed gas bubbles are trapped by cavities formed in the heat exchange surfaces where boiling of the oxygen takes place. Each cavity is of such a size and shape that the trapped bubbles grow until they break away from the cavity leaving residues of vapor therein sufficient to allow further gas to accummulate by evaporation until again bubbles break away.