A coal preparation plant typically operates with multiple cleaning circuits to clean individual size fractions of run-of-mine coal. Coal preparation plants are traditionally optimized using the equalization of incremental product quality approach. Individual cleaning circuits are operated at the same specific incremental product quality so that the targeted overall plant product quality is achieved. Over the years, it has been well established that equal incremental product quality approach maximizes plant-yield for a given product quality constraint. However, while dealing with multiple quality constraints, the incremental quality approach may not provide a complete solution to the optimization problem. It may be intuitive to realize that the dirtiest particle(s) in a coal product, with respect to ash content, may not be the same particle(s) with respect to sulfur content. Therefore, with increasing number of product quality constraints, which may include (but not limited to) limiting ash, sulfur and trace element contents, the plant has to be optimized based on each incremental product quality. Understandably, the operating points selected for each circuit to maximize plant-yield based on incremental ash content, may not be suitable for obtaining maximum plant yield based on incremental sulfur content. These limitations of the equalization of incremental product quality approach to satisfy multiple product quality constraints have been reviewed in detail in this publication with an example of ash and sulfur data collected from an operating coal preparation plant. (c) 2005 Elsevier B.V. All rights reserved.