slurry having an upper region and a lower region the catalyst concentration in the upper region of the slurry bed will contain less than about 20 wt of catalyst solids preferably the solids concentration in the slurry will be less than 10 wt and most preferably the solids concentration will be less than 5 wt for example fig5 shows two examples of the slumped bed operation where the solids concentration in the upper region of the bed range between about 20 wt and about 1 wt catalyst solids the catalyst concentration profile along the reactor height in the slurry bed will depend of course not only on the gas velocity but also on the catalyst particle size particle density total loading of the catalyst the height and diameter of the reactor and the slurry liquid density and viscosity the catalyst particle size refers to the effective catalyst particle diameter when used in this specification the bulk catalyst refers to catalyst particles having an average size greater than or equal to about 10 microns for example in the range of about 10 to 150 microns by fines is meant particles having a particle size below about 10 microns for example in the range of about 0 1 to 10 microns basically in the method of the present invention the fischer tropsch is operated in.