Carbon capture and storage and oxy-fuel combustion have recently become more significant due to global warming as well as green energy solutions. Oxy-combustion power plants fueled with natural gas are compatible with today’s clean energy policies. In this study, effects of oxygen content of reactant mixtures used in oxy-combustion on thermodynamic properties, adiabatic flame temperatures, combustion products and pollutant emissions are analyzed using a novel multi-feature equilibrium combustion model. Using natural gas from most important origins (Russia, USA, Iran, Australia) as fuel, results obtained from oxy-fuel combustion for three different O2 fractions are compared with the results of conventional air–fuel combustion for varying equivalence ratio, inlet temperature and pressure. The accuracy of the results is confirmed by two different popular combustion softwares. According to the results, oxy-fuel combustion of same oxygen content with air causes 24% less entropy production but 40 times less NOx emissions which is an indicator of significant decrease in carbon capture and storage costs. Comparison of natural gas of different origins shows that Russian natural gas is more advantageous in terms of NOx emissions where Australian natural gas is more advantageous in terms of entropy production.