The destruction of availability (exergy) during combustion processes is examined for an adiabatic, constant volume system. This is an analytical examination and did not involve experimental measurements. The fraction of the fuel's availability that is destroyed due to the irreversible processes is obtained as a function of temperature, pressure, and equivalence ratio for octane-air mixtures. In general, the destruction of the fuel's available energy due to the combustion process decreases for operation at higher temperatures. In addition, the effect of equivalence ratio on the destruction of availability is significant and depends on the particular operating conditions. Specifically, for the conditions of this study, the destroyed availability due to the combustion process ranged between about 5 and 25% of the original reactant availability. The implications of these results to combustion processes in internal combustion engines are described.