The product consists of three related macro-driven Lotus 1-2-3 spreadsheet programs and demo data for calculating the composition of a mixture that when added to the fuel produces a combined mixture (surrogate) that has a compositional profile and Carter MIR specific reactivity almost equivalent to that of automotive exhaust. Required inputs are speciated hydrocarbon data and oxygenate (alcohols and ethers) for the fuel and speciated hydrocarbon, oxygenate, carbonyl (aldehydes and ketones) and carbon monoxide data for the exhaust. The program compares the composition of the exhaust and the fuel, identifies and calculates the amount of exhaust components that should be added to the fuel so that the resulting mixture would closely approximate the characteristics of a real exhaust. The rationale for this approach is that the complexity of the exhaust mixture results mainly from the fuel (i.e., combustion derived components are relatively small in number). The compositional and reactivity profiles of the exhaust can be readily approximated by the addition of less than 20 combustion identified exhaust components to the fuel.