The research described in this paper was conducted in support of a more extensive study that has been ongoing at the University of Calgary to quantify the effect of the presence of low levels of oxygen in the unheated portions of an Athabasca Reservoir undergoing in situ combustion, and to evaluate if low temperature oxidation reactions could be used to achieve in situ upgrading. The objective of the overall program was to understand the compositional changes that might occur at temperatures ranging from those of the native reservoir to those experienced in a steam injection oil recovery process. The research program was originally started to quantify what were anticipated as detrimental compositional changes when oil is oxidized at native reservoir temperatures. The program was then extended to quantify the possible enhancement of the rate of cracking which might be achieved by oxidizing the oil at low temperatures, then heating it to temperatures typical of a steam injection operation. This paper will concentrate on the compositional changes of Athabasca bitumen in contact with nitrogen and air. The experiments were performed in an oscillating batch reactor with or without core and synthetic brine. The rate of oscillation was evaluated as a parameter to examine the role of mass transfer rates. Viscosity is reported in addition to the compositional data expressed in terms of the components: maltenes, asphaltenes, and coke. The data has direct applicability to recovery processes involving the injection of air or a gas containing oxygen as an impurity. Typical applications of this nature include in situ combustion, flue gas injection, and replacement of a gas cap with air or injection of CO, containing oxygen as an impurity.