The influence of different assumptions for thermochemistry modeling in hypersonic flow over a double-cone geometry is investigated. The double-cone geometry is simple but produces a complex shock wave/boundary layer interaction and nonequilibrium flow physics. This interaction sig-nificantly impacts the aerothermodynamic loading, in terms of surface pressure and heat transfer. Therefore, it is important that these interactions can be predicted with physical accuracy and numerical efficiency. A CFD analysis is used to study the double-cone in three different thermochemical cases: nonequilibrium flow, equilibrium flow, and frozen flow for five different mixtures of nitrogen and oxygen. Specific areas of interest include the thermochemistry model effects on the flow field and surface properties. The resulting aerodynamic loads are compared to experiments and indicate that thermochemistry modeling assumptions play a significant role in determining surface properties. It is also shown that heat loading is more sensitive to thermochemical modeling than drag and suggests that an accurate measurement of surface heat transfer is of particular interest. Careful analysis also reveals that high enthalpy and pure oxygen flows are particularly sensitive to the thermochemistry model assumed.