The synthesis of multipurpose heat-exchanger networks that are capable of operating two plants stand-alone as well as integrated is presented. Designs for direct integration using process streams and indirect integration using intermediate-fluid circuits are obtained. The mathematical models proposed in the synthesis of these designs account for unassisted and assisted forms of integration, and they rely on results previously obtained in a targeting phase. Finally, an economic comparison between the two types of integration for a realistic case of a crude unit and a FCC unit is performed. The analysis also reveals that the widely accepted statement that indirect integration using steam can achieve most of the energy savings in the total site is not valid when compared with an intermediate-fluid circuit.