Efficient cogeneration is widely acknowledged as one of measures reducing primary energy use and emissions of greenhouse gases and other pollutants. This contribution bears on analyses of complex industrial power plants, incorporating the concept of exergetic and exergoecomic balances – a concept that has been rarely utilized in Slovakia up to day. Emphasis is laid on synergic use of marginal and exergoeconomic analysis, thus assessing the economics of various complex cogeneration units’ operational modes. The whole study, together with resulting recommendations for cogeneration efficiency improvement of the given unit is an excerpt of corresponding author’s doctoral thesis.