The pressure effect on the product distribution in the cobalt-catalyzed Fischer-Tropsch synthesis was investigated using a deuterium/hydrogen switching method with a fixed bed reactor. Reliable results were obtained at relatively high reactant conversion. On increasing the operating pressure from 0.2 to 2 MPa, the chain growth probability increased from 0.83 to 0.90, while the selectivity for methane and branched products decreased. Moreover, the obtained paraffin/olefin ratio increased with an increase in the carbon number, but was nearly constant at higher pressure. This study shows that higher chain growth probability and more olefins could be obtained under elevated operating pressure. (C) 2007 Elsevier B.V. All rights reserved.