Abstract: The present invention provides a reaction system for a Fischer-Tropsch synthesis which has high mass transfer characteristics at the catalyst. The reactor comprises a monolithic catalyst comprising a solid body defining discrete and continuous channels extending from one end of the body to the other. The walls of the channels contain a conventional Fischer-Tropsch catalyst; conventional promoters may also be included. The body preferably may also comprises channels for conducting coolants which are arranged traversely to the reaction channels.