The Multicomponent, One-Dimensional, and Compartment-Based Dynamic Model Developed by Rados Et Al. (Catal. Today 2003, 79-80, 211-218) Has Been Used to Study the Performance of Slurry Bubble Columns Operated with Two Chemical Reaction Systems. One Reaction Causes Contraction in the Gas-Phase Volume, and the Other Causes Expansion. the Change in the Gas Flow Rate (Expansion or Contraction) Along the Reactor as a Result of the Chemical Reaction Kinetics is Accounted for by the overall Mass Balance of the Gas Phase Represented by Large and Small Bubbles. the Importance of Properly Accounting for the Change in the Gas Flow Rate Has Been Demonstrated. the Back mixing in the Three Compartments of the Model (Small Bubbles, Large Bubbles, and Slurry) is Accounted for by the Axial Dispersion Model. the Effects of Operating Conditions and Reactor Dimensions on the Slurry Bubble Column Performance Have Been Evaluated. a Detailed Analysis of the Role of Back mixing on the Performance of the Fischer-Tropsch Synthesis (Contraction of the Gas Phase) Has Been Conducted by Varying the Axial Dispersion Coefficient (E) of the Three Phases between Ideal Plug Flow (E = 0) and Completely Mixed Flow (E = ∞). © 2005 American Chemical Society.