The aim of deregulation in the electric power industry is to optimize the system welfare, by introducing competitive environment, mainly among the suppliers. Developing fair and equitable real and reactive power allocation method has been an active topic of research. This book suggests current methodologies to allocate real and reactive power output of individual generators to system loads and flows. Allocation procedures presented can be used independently in deregulated power systems. The choice of the chosen algorithm depends on their limitations and suitability. The advantages of various methodologies are demonstrated on commonly used test systems. The new methodologies provide better reliability and minimize the limitations of conventional methods. The presented methods could be used by independent system operators and engineers to resolve some of the difficult real and reactive power pricing and costing issues and to ensure fairness and transparency in the deregulated environment of power system. Furthermore, the ideas developed in this book can be utilized for educational and research purposes such as loss allocation and congestion management in deregulated power systems.