Simulation of a single tube of a wall-cooled multitubular Fischer-Tropsch (FT) reactor with a cobalt catalyst indicates that the reactor performance is improved by enlarging the catalyst particle diameter. This aspect is studied for variation of the particle size for a fixed tube diameter and vice versa. For a syngas conversion per pass of about 30?% as target and a typical industrially used single-tube diameter of 40?mm, a particle size of >?3?mm is appropriate with regard to a high production rate of higher hydrocarbons. For a particle diameter of