A process for the preparation of hydrocarbons by catalytic reaction of carbon monoxide with hydrogen in which reaction a feed comprising hydrogen and carbon monoxide is contacted at elevated temperature and pressure with a catalyst comprising cobalt and manganese in which catalyst the cobalt/manganese molar ratio is between 14:1 and 7:1 and the GHSV is at least 1600 N1/1/h. Preferably the cobalt/manganese molar ratio is between 13:1 and 9:1 and the GHSV is between 2700 and 25,000 N1/1/h. The reaction is especially carried out in a slurry phase regime.