The objective of this research is to demonstrate the feasibility of sustained combustion in hybrid rocket motor configuration with oxidizers containing high concentrations of CO2, an in situ propellant suitable for Mars applications. Motor tests are performed by using N2O/CO2 mixtures as the oxidizer and paraffin fuel loaded with high concentrations metal powders. Fuel grains with aluminum and magnesium powders have been cast at 40% by mass in the paraffin wax binder. CO2 is mixed with liquid N2O up to 50% in weight percentage as a saturated liquid mixture. Experiments are performed in the blowdown mode using the self-pressurizing capability of the mixed oxidizers. A labscale hybrid motor with 70 mm grain length and 31 mm outer grain diameter is used to measure the key performance parameters such as regression rate and combustion efficiency. Successful ignition and sustained/stable combustion with the mixed oxidizer are achieved at CO2 concentrations up to 43% by mass in the liquid mixture. The primary conclusion from this study is that the operation of hybrid rockets with substantial levels of in situ propellant CO2 is feasible.