TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: The liquid medium is added and withdrawn from the reaction zone to create a flux which facilitates the bed expansion to the point where at least some of the solid catalyst is in a state of random motion. The gases are introduced at a predetermined distance(s) from the vessel bottom, preferably 3-8 or especially 6-7 predetermined distances. The gas is introduced through a sparger attached to a tubular section extending inward through the wall of the reactor. The diameter of the sparged bubbles of synthesis gas is less than 5 mm. The liquid medium is paraffin wax and/or hydrocarbons of b.pt. 150-340 degreesC. There is a device for modifying for liquid medium and/or catalyst during the reaction. At least part of the liquid medium that is withdrawn is recycled. The concentration of middle distillate fraction of b.pt. 200-340 degreesC in the recycled liquid medium is 0.001-50 vol.%. The solid particulate catalyst has average particle diameter of 0.2-3.5 preferably 0.3-1.6 mm and the molar ratio of hydrogen:carbon monoxide is 0.5:1 to 6:1 preferably 1:1 to 3:1 and especially 1.6:1 to 2.2:1. The reactor vessel contains a unit for removing heat which is preferably a tube arranged such that a cooling medium can enter and exit the tube from outside the reactor vessel. The cooling medium is a liquid which is at least partially vaporized within the tube, selected from Dowtherm, water and/or glycols. There is a device external to the reactor for removing heat from the liquid medium to be recycled. The gas space velocity is 200-20,000 preferably 500-10,000 m3/m3 catalyst per hour. The liquid flux is 1-10 cm/sec. The liquid space velocity is 10-100 preferably 20-80 m3 inert liquid/m3 catalyst per hour. EXAMPLE - 1000 standard cubic feet per hour of synthesis gas containing 46.8 mol.% nitrogen, 33.1 mol.% hydrogen, 16.8 mol.% carbon monoxide and 0.32 mol.% water vapour was contacted with 0.61 cubic feet of a cobalt ruthenium catalyst on alumina support at an average reactor temperature of 204 degreesC, a pressure of 370 psi and a gas hourly space velocity of 1650 cubic feet per hour per cubic foot of catalyst. An 85% conversion of CO to hydrocarbons was achieved under these conditions in a single pass through the reactor. The hydrocarbon product stream had the following composition (wt.%, lb/hr): Methane (8.08, 0.45); Ethane (1.90, 0.11); Propane (2.57, 0.14); Normal butane (3.04, 0.17); Normal pentane (3.42, 0.19); 6-12C hydrocarbons (27.28, 1.51); 13-19C hydrocarbons (23.10, 1.28); 20+C hydrocarbons (30.61, 1.70).