In a gas-solid circulating fluidized bed (CFB), solids are fluidized as dispersed particles and aggregated clusters. Aggregated clusters are much denser and much larger than dispersed particles, significantly influencing reactor performances. Even though many studies have already been conducted on cluster characterization, key cluster properties have a variation up to an order of magnitude, severely hindering the understanding of CFB. In the literature, cluster information was extracted from experimental data using a variety of discrimination methods. The way to identify clusters has essential impacts on cluster properties. A thorough discussion on cluster definitions is imperative, but remains lacking. In this work, discrimination methods are reviewed, tested on sample data and discussed with verified phase classification. It has been found that existing discrimination methods characterize different phases, resulting in severe discrepancy. To settle the discrepancy on cluster properties, a discrimination guideline has been proposed for phase discrimination in circulating fluidized beds. (C) 2020 Elsevier B.V. All rights reserved.