Аннотация:An energy transmission system is usually a part of every energy market. The problem of optimizing transmission system to maximize the social welfare is the subject of the present paper. For energy markets with tree-type network structures, an approach to optimizing their transmission systems is developed based upon the concept of competitive and complementary network lines. Also, a method for the supply–demand balances transfer to the root node of the network is discussed. Finally, the problem of optimally developing an energy transmission system up to a given planning horizon is discussed.