This paper analyzes some of the chemical and kinetic principles that rule the automatic generation of reaction mechanisms by the system EXGAS for the oxidation of alkanes. The systematic inclusion in the mechanism of all possible reaction pathways, in comparison with other models published, permits one to discuss the role of the different classes of reactions and to deduce some methods for simplifying a priori these mechanisms from a kinetic basis. The first technique is based on an analysis of the reactivity of free radicals and of the relative rates of generic reactions versus temperature. This analysis of reaction rates allows us to discuss the temperature ranges where it is necessary to consider one or two successive additions of an oxygen molecule to a hydrocarbon radical when modeling the oxidation of alkanes. A method to decrease the number of species and reactions deriving from the second addition of oxygen is also reported. Substantial reductions of the number of reactions and species included in the primary mechanism can be attained by these techniques. The validity of the simplified mechanisms obtained by these methods is illustrated with some examples derived from the modeling of the oxidation of n-heptane and n-decane.