Agglomeration is used to generate particles of specific sizes, reduce dust emissions and stabilize particulate mixtures. In Fluid Cokers, which upgrade heavy oil through contact with hot coke particles, agglomeration increases reactor fouling. The objective of this study is to understand how the stability of a wet agglomerate in a fluidized bed is affected by its liquid content, its location and the size of its particles. Agglomerates were made of fluid coke and biodiesel, the shear force required to break them was measured with a new device and agglomerates were introduced in a fluidized bed. The stability of a wet agglomerate in a fluidized bed depends on its liquid content, its bulk density and the Sauter mean diameter of its constituent particles. Increasing liquid content or bulk density increases agglomerate stability while increasing the Sauter mean diameter of its particles reduces its stability. Artificial agglomerates were made from polyurethane foam, magnets and an RED tag. Agglomerate breakage and location could be detected with an RFID reader. It was found that bigger and denser agglomerates spend less time on the upper surface of the bed. The average survival time of an agglomerate in a fluidized bed is proportional to the critical shear force required to break the agglomerate. (C) 2012 Elsevier B.V. All rights reserved.