Deregulation of power markets in Europe will facilitate competing alternatives in power supplies, more competitive energy prices and will improve customer service. The Romanian power sector is also characterized by profound transformation from old, polluting system to one reaching for efficiencies of market-driven economy. In order to reduce the production costs of combined electricity and heat generation power plants, the paper presents the software called CTO for optimization of the cross-current cooling tower's operation. The optimum operation of the cooling tower will be that which performs the removal of the waste heat-of imposed thermal level- at a minimum specific cost. For different alternatives of the known input values and for all possible operation diagrams the cooling tower parameters are calculated through the developed software. As a result its optimum operation conditions are indicated.