Thermoeconomics is a discipline that connects Thermodynamics and Economics concepts, usually used for rational cost assessment partition to the final products of a thermal plant, by means of a model that describes the cost formation process of the overall system. Generally, exergy or monetary costs of the external resources are distributed to the final products. However, environmental consideration can be incorporated in the models to calculate the environmental costs, such as specific CO2 emission of each final product. This work aims at showing how the thermoeconomic models can be adapted to allocate the overall CO2 emission of four different gas and steam turbine cogeneration systems to the final products (net power and heat), in order to determine the specific CO2 emissions (in g/kWh) of each product. This subject is important in applications of Life Cycle Assessment encompassing processes with two or more products and also in quantifying the cogeneration environmental advantage. This paper also reveals that any thermoeconomic model can be easily adapted for allocation of the overall CO2 emissions or any other pollutant to the final products of a cogeneration or multi-product plant.