A Monolithic Loop Reactor design for Fischer-Tropsch synthesis with a production capacity of 5000 ton middle distillates per day (about 40 000 bbl/day) is presented. The required volume, 3350 m3, is competitive with conventional reactors, while eliminating disadvantages of existing reactor types such as catalyst attrition and separation, backmixing and large diffusion distances. Although the kinetic expressions used in this study do not allow calculating the selectivity precisely, all important conditions, low temperature rise and constant H2/CO ratios, are met to ensure high selectivity towards heavy hydrocarbons.