This study presents an analysis of an existing biogas engines powered cogeneration system installed in Varna Wastewater Treatment Plant, Bulgaria using thermoeconomic method. The thermoeconomic analysis is conducted using three different groups of environm ental conditions. The SPECO (specific exergy cost) method is applied to the system and cost balance equations are formulated for each component. The fuel F and the product P rules are used to obtain auxiliary equations. Moreover, in this paper, various the rmoeconomic performance parameters such as the cost of exergy destruction, the relative cost difference and the exergoeconomic factor are determined. The obtained results show that the specific unit exergetic cost of the electrical power produced by the co generation system are found to be 30.0 GJ = 0.1 1 €/kWh, while the conducted thermoeconomic analysis based on energy delivers a result of 0.1 9€/kWh for the electrical work produced by biogas engines. In addition, the obtained results are compared to those s een in similar studies.