Studying accelerated bitumen aging in the laboratory on a kinetic basis leads to evaluating the activation energy of oxidation reactions from developments in certain characteristics such as asphaltene content, penetration, and ring-and-ball softening point. In Belgium, temperatures 5 mm deep in bituminous road pavements have been measured and recorded for several years, thus making it possible to draw a frequency distribution curve of those temperatures. From this distribution and the activation energy evaluated in the laboratory, it has been established that the annual value of kinetic mean temperature lies around 19.5 deg C for field aging. Using measurements of bitumen chanacteristics published in the literature, and referring to the original condition as well as the conditions at the time of opening to traffic and at various stages of aging, the reaction constants can be estimated for the road pavements under consideration. This approach enables the estimated constants to be related to the specific climatic environments of the various countries or regions concerned.