Industrial Symbiosis entails the transformation of linear industrial processes into closed loop systems: matter and energy flows that were wastes become resources for other processes (by-products), resulting in a reduction of both natural resources consumption and waste production. Thermoeconomics has two key advantages as analysis method for Industrial Symbiosis: it provides a systemic and rigorous framework and, due to the use of exergy for flow quantification, streams of different nature are measured in the same unit. The goal of the paper is to analyze in depth the process of exergy cost formation of flows within a system, which change when it is integrated with other systems, by using two complimentary approaches. First, a strategy based on irreversibility of the different components and effects of waste internalization already developed is applied for the first time to an example of Industrial Symbiosis. Second, a new method tracing the origin of the different resources consumed by the system is developed. This approach is very interesting for Industrial Symbiosis examples, characterized by a diversity of resources. A system composed of a coal-fired power plant, a cement kiln and a gas-fired boiler operating in isolated and integrated fashion is analyzed by using both presented approaches. (C) 2012 Elsevier Ltd. All rights reserved.