The combustion, oxidation, and pyrolysis chemistry of even simple light hydrocarbons can be extremely complex, involving hundreds or thousands of kinetically significant species. Even relatively minor species can play an important role in the formation of undesirable emissions and byproducts, and their properties and reactions need to be modeled in some detail in order to make accurate predictions. In many technologically important applications, the reaction chemistry is closely coupled with the mixing and heat flow, dramatically increasing the computational difficulty. The most reasonable way to deal with this complexity is to use a computer not only to solve the simulation numerically, but also to construct the model in the first place. We are developing the methods needed to make this sort of computer-aided kinetic modeling feasible for real systems. The computer is used to calculate most of the molecular properties and rate parameters in the model by a variety of quantum- and group-additivity-based techniques. We summarize our new computer methods for modeling the pressure dependence (falloff and chemical activation) of gas-phase reactions. Our approach to determining the optimal reduced kinetic models for various reaction conditions is discussed, Adaptive-chemistry methods that allow one to solve detailed macroscopic reacting flow simulations involving hundreds of species are outlined.