The aging in the course of the years of asphaltic bitumen used in bituminous constructions has various causes. One of these, the action of oxygen, is the subject of this publication, although in particular the investigation relates to the rate and intensity of aging caused by the action of oxygen under pressure and without the presence of light. The chemical reactions involved, however, are not dealt with. The investigations showed that of the various factors which could serve as the most suitable basis for a quantitative examination of the phenomena of aging, the penetration was preferabie to the ring and ba1l softening point, the ether asphaltenes content, or the increase of weight. In evaluating the general results, attention is paid to the shape of the aging curves, and an attempt is also made to explain what happens when the aging procedure is interrupted and then resumed after remixing the batch. From the study it has been inferred that asphalts may be prepared which are much less liable to aging than normal ones of the same grade. The probability of parallelism between natural and artificial aging has also been shown by the results of some of the experiments. The experimental part of the investigation consisted of keeping thin layers of various types of asphaltic bitumen in oxygen at 60°C. and 20 atm. for a varying number of days, and then measuring the changes in the penetration figure, the softening point and other similar characteristics. In addition, several practical experiments relating to the influence of the atmosphere were carried out (natural aging). The materials used were asphaltic bitumens, either as such or mixed with filler, oil or rubber. The results have shown that the characteristics measured, such as the penetration figure and the softening point, altered most quickly at the beginning of the experiments, but that those changes, and therefore the aging rates of the asphaltic bitumens, subsequently became slower and slower. Although the number of available data relating to experiments with natural aging is fairly smalI, it can be assumed that natural and artificial aging proceed in similar ways. Further investigations into the re1ationship between the characteristics measured and the length of time lead to the hypothesis that aging proceeds differently during all. initial period of about 7 days from the way it does subsequently, when it has the nature of a unimolecular reaction. The question of whether it is possibie to manufacture asphaltic bitumen of a given hardness which is less than normally sensitive to the aging influence of oxygen can, on the evidence of experiments with "stepped" or interrupted aging, be answered in the affirmative: if a soft asphaltic bitumen is artificially aged until the desired hardness is reached, the result is a product of which further aging under the influence of oxygen is less rapid than that of untreated asphaltic bitumen of the same hardness. The influence of temperature and pressure, as well as that of the thickness of the layer, in the accelerated aging experiments has also been investigated. The trials dealing with the layer thickness, indeed, produced remarkable results which can perhaps be explained by the occurrence of the phenomena of de-mixing and convection in thick layers of asphaltic bitumen. Finally, several other experiments on the artificial aging of asphaltic bitumen mixed with macadam are discussed, showing that in such cases aging does not proceed in exactly similair ways for different types of asphaltic bitumen. It was also found that a mixture of asphaltic bitumen andtar ages more quickly than pure asphaltic bitumen does, particularly in the initial period.