High seed quality is a prerequisite for successful crop production, making maintenance of seed viability and vigour during storage important. The effects of temperature and humidity on seed ageing are well known, while the negative effect of oxygen in the seed storage environment has been studied less. Here we report on experiments to study the quantitative effect of oxygen on the ageing of seeds. Primed celery seeds were chosen as a model, because of their relatively short shelf life. After equilibration at four relative humidity levels (16, 33, 43 and 60% RH), the seeds were stored at four temperatures (5, 13, 20 and 30°C) and six oxygen levels (1, 5.2, 10, 21, 50 and 99%) for a period up to seven years. Germination tests after storage confirmed a strong shelf life-extending effect of low oxygen conditions, at all four temperatures and the three lower humidity levels. Modelling the viability data revealed a linear double logarithmic relationship between the oxygen concentration and the storage time till a 50% decline in viability (p50), for seeds pe-equilibrated at 16, 33 or 43% RH. The models also showed that each halving of the oxygen concentration increased seed longevity by around 77%. This means that a reduction of the environmental oxygen concentration to a level below 1% increased the shelf life of the primed celery seeds by a factor of twelve. For seeds pre-equilibrated at 60% RH, the effect of lowering the oxygen concentration below 21% was much less or even absent at 30°C, likely due to a different physical or physiological condition of the seeds at this higher humidity level. The large and logarithmic effect of reducing the oxygen level during the dry storage of seeds provides additional opportunities to prolong the shelf life of seeds either for commercial or genebank storage. To estimate the effect of these factors, a model is provided describing the quantitative effect of all three factors, temperature, equilibrium relative humidity and oxygen concentration. Several options for practical application are discussed.