The thermal performance of power generating and consuming devices can be improved significantly, both during design and operation. Turkey's electric energy demand is growing at an average of 6-8% yearly. Cogeneration facilities have an important role in the country's energy strategy, because a substantial amount of Turkey's energy need has been met by cogeneration facilities in recent years. In the present study, the chemical and physical exergy and exergy destruction of the cogeneration system was calculated with the BASIC program by using second law analysis. Performance of the cogeneration system is also discussed, based on the second law (exergy) concept.