Reactant (CO and H-2) concentration and conversion profiles were determined as a function of axial distance for the Fischer-Tropsch reaction in a slurry bubble column reactor. Model equations were developed from the basic concepts, i.e., conservation of mass and momentum, and combined with iron catalyst reaction kinetics as well as mass transfer coefficients, gas, liquid, and solid phase holdup, Henry's Law constants, minimum fluidization velocity, and terminal velocity obtained from empirical correlations. Concentration profiles and conversion were-determined for varying key process variables: liquid-phase velocity and rate constant. Results suggest that the reaction is kinetically limited and that conversion is proportional to liquid velocity. Thus, process improvements can be achieved by either maximizing liquid-phase velocity or increasing the rate constant by modifying the catalyst.