The performance of steam power plants, utilizing recovered waste heat from air-fuel and oxy-fuel combustion, are compared. Temperature profiles in the heat recovery steam generator (HRSG), steam production rate, net-work output and energy efficiency are simulated for different conditions. Investigations are made into the effect of varying pinch point on HRSG performance, net-work and energy efficiency for power generation utilizing oxy-fuel combustion. It is found that with increased pinch point there is an associated decrease in HRSG and steam plant efficiencies. Exhaust gas composition influences the energy efficiency of the power plant. When air-fuel and oxy-fuel combustion are compared there is a reduced amount of nitrogen in the oxidant stream in the latter case. When comparing air-fuel and oxy-fuel combustion, a considerable deviation in HRSG and steam power plant performance is exhibited, with oxy-fuel combustion offering benefits in system efficiency and plant output. The exhaust gas composition at the HRSG inlet contributes significantly the performance characteristics of the system. Raising the HRSG inlet temperature also increases power generation and system efficiency. The results provide insights into the use of oxy-fuel combustion for systems utilizing HRSG for power generation while demonstrating the influence of gas composition, pinch point, and exhaust gas temperature on system performance, and suggest that oxy-fuel combustion can help enhance the contribution to sustainable development of some energy systems.