Abstract: A gas mixture containing significant proportions of nitrogen and oxygen, such as atmospheric air, is alternately passed through two adsorbers containing a carbonaceous molecular sieve such as comminuted coke. With one-minute half-cycles, each half-cycle encompasses a production phase of 55 seconds during which the gas mixture is driven under high pressure through one adsorber with recovery of high-purity nitrogen therefrom while the other adsorber is being exhausted or vented in a regeneration phase. During a small fraction of the remaining 5 seconds of this half-cycle, preferably lasting between 0.3 and 0.7 second, the two adsorbers are interconnected for a partial equalization of their pressures. In the final period of slightly more than 4 seconds, the regeneration phase of the first adsorber begins while the second adsorber is pressurized with fresh gas mixture, its outlet being closed at that time.