Population balance models can be used to understand the pathway of fines generation in both the FCCU and the laboratory setting. Analogous to a reaction kinetic model, this technique can be used to distinguish the relative rates of attrition via particle fracture versus abrasion. A population balance model was applied to FCCU to assess the importance of different catalyst attrition mechanisms. Fracture and abrasion were found to occur in commercial units, however, in five out of six units, abrasion was most important. This same technique was subsequently applied to several laboratory attrition methods. An air jet method was identified as being the most relevant. Using a single sample of equilibrium catalyst, attrition in the different tests were found to ranged more dramatically, from predominantly fracture to mainly abrasion-based attrition. This is an abstract of a paper presented at the NPRA 2011 Annual Meeting (San Antonio, TX 3/21/2011).