A semidetailed kinetic model consisting of 225 free radical reactions has been developed to describe the thermal cracking of n hexadecane mixed with tetralin or toluene. The model was tested against available experimental data in the temperature range 360-440 degreesC. The observed inhibiting effect of tetralin and toluene is explained by the formation of radicals stabilized by resonance, via H transfer processes, that lead to new termination reactions. A "factor of inhibition" FI is defined to measure the inhibiting effect of an additive on the decomposition of an alkane. This factor FI depends on the resident time, the concentration of the additive, the temperature, and the thermal stability of the inhibitor. For the mixture n hexadecane-tetralin, the inhibiting effect increases when the temperature increases, whereas the inhibiting effect increases when the temperature decreases in the case of toluene. The comparison between tetralin and toluene shows that toluene may be considered as a pure inhibitor contrary to tetralin. Indeed, during the pyrolysis of tetralin, the formation of molecules such as 1 methylnaphthalene, naphthalene, or butylbenzene, which accelerate the chain mechanism by forming several new radicals by bimolecular initiation reactions, reduces the inhibiting effect of tetralin. A theoritical study of the mechanism of acceleration and inhibition of alkane pyrolysis was treated and led to a better understanding of interactions in a mixture.