Pollution-free or low pollution, efficient, large scale electrical power generation systems, using thermal energy from combustion of hydrocarbon fuel are described herein. The pollutant-free hydrocarbon fuel is combusted in a gas generator with pure oxygen or substantially pure oxygen that is free of nitrogen. Water is also injected into the gas generator. The gas generator discharges high enthalpy steam and carbon dioxide which can then be utilized in a variety of applications, including driving turbines for power generation. The steam can be recycled into the gas generator or discharged for various uses. The carbon dioxide can be collected for industrial use or discharged.