Publisher Summary This chapter introduces O2/CO2 concept to commercial data from an 865 MWe lignite fired reference power plant and large air separation units (ASU). O2/CO2 combustion involves burning the fuel in an atmosphere of oxygen and recycled flue gas instead of in air. The mixed flow of oxygen and recycled flue gas is fed to the boiler together with the fuel, which is burnt as in a conventional plant. Typically, 70-80% of the flue gas is recycled from down stream the economizer and mixed with new oxygen. The remaining part of the flue gas is cleaned, compressed and later transported to storage or to another application. Studies on O2/CO2 combustion have mainly concerned emissions and combustion behavior. It identifies essential components and energy streams of the two processes and investigates the possibilities for process integration. A detailed design of the flue gas treatment before transportation of the separated carbon dioxide has also been proposed. The sulphur dioxide can be sequestered together with the carbon dioxide, provided that the gas is dry, and, consequently, there is no need for a desulphurizing unit. Because the investment cost of an ASU is slightly lower than for the desulphurizing unit, the investment cost of the O2/CO2 plant will be slightly lower than for the reference plant. With all identified integration possibilities the net electrical efficiency becomes 34.3%, which is a reduction by 8.3 percent units compared to the reference plant.