CO2 capture and storage in hydrocarbon reservoir seems to be a good solution to reduce greenhouse gas emissions. However, combustion residual gases are not only composed of CO2 but also associated with minor gases. In the case of oxy-combustion, the main minor gas is oxygen in elevated proportion (up to 7%). O-2 injection can induce hydrocarbon oxidations and hence it is necessary to evaluate its consequences on the storage. Hydrocarbon oxidations were studied with a double approach: experiments and kinetic modeling. In a first step, pyrolysis of a model hydrocarbon (n-hexadecane) in CO2 atmosphere reveals no chemical reactivity between hydrocarbons and CO2. Experimental oxidations were then carried out by injecting artificial air in a closed reactor on: (i) a pure n-alkane (n-hexadecane) and (ii) a natural crude oil. Results of both experimental and numerical modeling showed two oxidation types depending on temperature: a low oxidation, and an auto-ignition. The simulation results were globally in agreement with experiments but need to be adapted to low temperature-high pressure conditions. The preliminary findings of this investigation emphasize on the oxidation consequences: (i) on oil composition and (ii) risk (auto-ignition) in context of gas mixture injection (CO2/O-2) in petroleum system.