Abstract: The present invention relates to a method and a system for producing a mammalian pre-embryo and a stem cell having a better quality than prior art methods. The system comprises means for obtaining a mammalian oocyte, and means for obtaining a mammalian spermatozoa, and an apparatus having at least two separate air-tight chambers, for which the oxygen tension of one chamber may be changed independent of the oxygen tension of the other chamber, said at least two separate air-tight chambers constitute a main chamber and at least one residence chamber.