We used a batch reactor to conduct the Fischer-Tropsch reaction on a Co/TiO2 catalyst without charging any liquid in the reactor tank. The catalyst was loaded in a fixed catalyst basket, and the reactor was operated as a "gas-solid" reaction system. Before entering the batch operation for the reactor, it was initially operated under CSTR mode. The reactor was controlled under 210 degrees C and 20 bar (g) of pressure with a 2:1 H-2/CO ratio in the feed gas when it was under CSTR mode. The time for the batch operations was varied between 20 min and 22.5 h. After each batch operation, the reactor was resumed to the CSTR mode for building up the same starting conditions for different batch operations. Both the selectivity to the olefmic and paraffinic products and the reaction rate were observed to increase when changing the operation from CSTR to batch mode. The reactor pressure was monitored and the comparison of the reading pressure and the pressure derived from the mass balance suggested that part of the product water was in the liquid phase in the reactor. Oxidation of Co might have happened when approaching the end of the batch operation.