This paper compares standard gas turbine combustion chambers and CO2-diluted oxy-fuel combustion chambers for a semiclosed combined cycle at a preliminary design level. To this end, simple chemical reactor networks, based on the well stirred reactor plus plug flow reactor scheme, are analyzed using the Cantera package and the GRI 3.0 chemical kinetics mechanism. The focus is put on the CO consumption process and the final CO concentration. The behavior of this model suggests the use of the adiabatic equilibrium temperature to characterize the composition at any station inside the chamber and the incipient lean blow-out equilibrium temperature to fix the well-stirred reactor volume. This model is applied to a feasible design point of a power production cycle (combustion exit temperature 1600 K, combustion pressure 30 bar). The fuel is a natural gas with an 87% by volume CH4 content, the ASU stream is a 95% O-2 gas, and the recirculated gas is an 82% CO2 gas. The residence times required for CO burnout are approximately 30% greater than those for air combustion for the same conditions, although the required lengths are much closer. The residence times and lengths would be reduced if the combustion exit temperature or the combustion pressure of the cycle was increased.