Neighboring networks need to be interconnected for many reasons, such as: the benefits of power sales in either direction across the boundaries which take the advantages of differential power demand according to time of day or seasonal/weather changes. Sharing resources in this way would defer installation of new generation, it would also involve sharing the provision of spinning reserve and reduce the hot standby reserve requirements. In any interconnected power system, the most important problem facing the power system operators is the management of their own power system transactions (buying or selling the electric power) to achieve maximum benefits from interconnection. Some computer programs have been produced to deal with this problem such as Multi-Systems Production Simulation Program (MAPS) package. The operators have to run four dependent programs to make a decision to sell or purchase elęçtric energy, which may take a long time and cause accumulated errors This p < /strong>aper produces a new computer program developed by using C++ language. The program deals directly with the mentioned problem and helps the interconnected power system's operators to take fast and reliable decisions. Whenever the power system has a missing load, the program can calculate the minimum cost to supply that load by coordination between the system reserves and purchasing energy from other interconnected systems. On the other hand, whenever the system has surplus generation energy the program can detect the available power to be sold to other systems and calculate approximately the price of sale. The program also, determines the units' commitment, and develops the generating units' priority list. Two example systems are used to show applications of the proposed computer program in both purchasing and selling models.