A unified model of gaseous fuel-air mixing is applied here to study the effect of shock waves on enhanced methane-air mixing. The model uses the fuel mass fraction within infinitesimal fluid elements and the total derivative of this fraction with respect to time to measure the degree and rate of mixing, respectively. The model is strictly accurate only for low-pressure combustors because of the ideal gas law assumption incorporated in the model. The model is also limited to gaseous fuels that contain single chemical specie, or behave like single specie. The model can be applied to any operational conditions or combustor geometry. Results show that mixing can be completed within the narrow region of the shock wave and therefore in a negligibly short time, if pressure, temperature and velocity distributions within this region are optimized. Furthermore, combining the effects of air preheat and shock waves can enhance both mixing with air penetration into fuel and fuel dispersion into the surrounding air. These results provide important guidelines for the design of supersonic combustors to achieve high efficiency and high intensity, while maintaining a low level of pollutants emission.