The establishment of permanent oscillations (“limit cycles”) has been often observed in the oxidation of several hydrocarbons in premixed, non-adiabatic systems like well-stirred reactors [1-3]. In such cases, the interaction between mass flow, heat exchange and chemical kinetics results in a periodic extinction and reignition of the system. Several operating parameters have been found to influence the establishment of periodic limit cycles: beyond the fuel type and the dilution level, the oscillatory behavior is affected by the reactor temperature, pressure and residence time. Thus, the high number of parameters makes theoretical analysis a necessary step to understand the causes of such phenomena. The simplest system to be studied is the combustion of hydrogen in a premixed reactor. Such configuration was first studied by Baulch et al. [2, 4, 5]. The oxidation of CO was also separately analyzed [6, 7]. In this work, a kinetic analysis of the hydrogen and syngas oxidation in isothermal, well stirred reactors is carried out. By adopting detailed kinetic mechanisms, the boundaries of the oscillating regions are defined through a parametric study. The Rate of Production (ROP) Analysis is adopted to understand the critical reaction paths.