A new experimental pairing method for multi-loop control is described in this paper. Unlike many existing methods, the proposed pairing rule is not based on generalized diagonal dominance, but rather on the passivity of the paired system. A frequency dependent passivity index is introduced to characterize the total destabilizing effect of both loop interactions and process dynamics. Based on this passivity index, pairing schemes that provide the best achievable control performance under decentralized control are chosen. (c) 2007 Elsevier Ltd. All rights reserved.