The National Energy Technology Laboratory (NETL) worked with Particulate Solids Research Inc. (PSRI) to con- duct the third CFD Challenge Problem in granular fluid flow to evaluate the progress and state of the art in sim- ulating gas solids flow in a circulating fluidized bed. Both Group A and B particles were tested at several gas velocities and solids circulation rates. For both particle groups pressures and particle velocities were measured within the riser. For the Group B cases local radial solids fluxes and high speed pressure fluctuations were mea- sured. Model predictions were compared against these experimental results and vetted in the workshop at the Circulating Fluid Bed X. The modelers were given detailed descriptions of the experimental facilities as well as physical property and small scale fluidization data on the different bed materials tested. Two general types of modeling simulations were submitted: Eulerian–Eulerian and Eulerian–Lagrangian. Both types of model had suc- cesses and failures indicating that good results are strongly influenced by resources such as available time, com- putational facilities, and experience level of the modeler. By comparing the predicted behavior the strengths and weaknesses associated with the different modeling approaches were identified and shortcomings could be targeted for future development and improvements.