In this paper, a new approach is proposed to design decentralized controllers for multi-unit plants that display nonlinear behaviour. The design method uses two measures that characterize stability and performance of a controller that has been derived from a particular design model. These measures are derived from robust control theory and permit the whole operating space, as determined by analysis of the disturbance variables, to be partitioned into sub-regions. The controller design models are derived by a consideration of the value of variables in a particular operating sub-region, as well as a particular decentralised control structure. In each sub-region, one controller is shown to produce increased stability and/or performance over other possible decentralised control structures.