One of the most common problems arising from the application of life cycle assessment is the allocation of environmental loads in processes yielding several useful products. This is the case for cogeneration plants, and in general, for any energy plant producing more than one useful energy flow. Since traditional solutions to the problem are unsatisfactory, two new approaches for this kind of allocation are presented in this report, both of them based on thermoeconomics. In the first one, allocation is based on the exergetic cost of the products, so that the formation process of energy flows is taken into account. The second one, which has been called 'method of the exergoenvironmental costs', is a refined version of the first solution. It differs as each environmental vector is incorporated in the balance at the exact point in the plant where it comes into play. These methods are a generalisation of thermoeconomics, extending the applicability of its propositions to the allocation of environmental burdens. A comparison between the different allocation methods and a discussion pertaining to their suitability are made. (C) 2003 Elsevier Science Ltd. All rights reserved.