The invention relates to a method for separating air by cryogenic distillation in a set of columns including a first column operating at a first pressure (21), a second column (23) operating at a second pressure which is lower than the first pressure and a third column (25) operating at a third pressure which is lower than the second pressure, wherein the third column includes first and second evaporator-condensers (29, 31) and nitrogen from a cold compressor (47) is sent to one of the evaporator-condensers.