This talk will present fundamentals and review of recent efforts in the development and validation of a combustion chemical kinetic mechanism for sCO₂ oxy-methane/natural gas combustion that can be used for computational fluid dynamic code (CFD) simulations in sCO₂ oxy-combustion development. Typical gas-phase combustion models for fuels (methane, natural gas, etc.) have been validated for gas turbine conditions – pressures below 40 atm and in fuel/air combustion- and cannot be extended to the operating conditions of sCO₂ combustors. Recent models are created by incorporating real gas and solvent effects on the combustion process using quantum chemical and molecular dynamic investigations. Validation is carried out using unique experiments conducted in CO₂ diluted methane/natural gas mixtures and for pressures up to 300 bar. Acquiring experimental data is critical in the development of a sCO₂ detailed kinetic mechanism as there was previously none available for methane at very high pressures near 300 bar (for Allam cycle) and for CO₂ diluted methane mixtures even at normal pressures. Simulations with reactor network modeling for the design of combustors for the industry will be discussed.