Concern about the effects of global greenhouse gases has made people aware of the need to reduce the atmospheric concentration of industrial waste gas. Alberta, as the centre of Canada's petroleum industry, is strongly impacted by the politics of greenhouse gases. One way Alberta can achieve the goals of the Kyoto Protocol is to capture CO2 from stack gases and to inject it into oil reservoirs to enhance recovery while sequestering at least a portion of the CO2. This paper will concentrate on oil from the Swan Hills Fonnation reservoir operated by Devon Oil Corporation. The phase behaviour of different concentrations of CO2/O-2 mixtures injected into the Swan Hills reservoir was investigated. Two PVT (Pressure-Volume-Temperature) apparatus were used to visually observe phases and to determine bubble points and swelling of the oil rich phase. The PVT measurements were performed to develop a basic understanding of the phase behaviour for the CO2/O-2/oil system. The composition of oxidized oil was predicted using a previously developed low temperature oxidation model coupled with phase equilibrium calculations.