[en] The Thermal Power Plant 'Negotino' is one of the biggest power stations in Macedonia built in order to satisfy the energy needs of the state. As an energy source it can operate on both fuel oil and natural gas. This paper deals with the correlative dependence of the ecologic parameters connected to the choice of the energy source. The usage of predefined type of fuel in large power stations establishes some ecological problems which need to be solved during the definition of technological parameters. The growing energy consumption and the need of electric power production in some periods of the year, is not the crucial factor in the process of the base fuel decision. The choice of the fuel must take into account the existing regulations for the environmental protection. (Original)