CO2 concentration in sausages packed under ambient air was between 3.82 and 3.93% at day 0. It remained roughly constant through-out the storage duration in pressurized samples whereas it increased up to maximum of 46.10% at day 21 for control samples. From day 14, a reverse tendency could be obtained between the CO2 content and the O2 content in the headspace of trays conditioned under air, as the former was shown to drastically increase whereas the latter significant-ly decreased. The consumption of O2 leading to production of CO2 is obviously due to respiration of microorganisms. On the other hand, the CO2 level remained stable in pressurized products packaged under air throughout the storage as it was observed for pressurized products packaged under MAP, but at an upper level. This would attest again for the presumable link between alteration of gaseous composition of packages and growth of microorganisms.