Minimum fluidization and bubbling velocities were used to compare the fluidity of FCC catalyst sourced from various refineries. It was found that fluidity characteristics of the catalyst of the same original type change after some period of use in the FCCU. Under closer examination using Scanning Electron Microscopy (SEM), large surface ridging of metal contaminates, was identified on the used catalyst. Mild bubbling attrition tests were conducted, and it was found that all of the catalyst experienced an increase in fluidity. Using total levels of iron, it was discovered that it is the quantity of metal ridging that is important and not the total levels of metals which influence fluidizing characteristics. This work provides insight into what causes changes to fluidizing characteristics inside an operation FCCU.