This work investigates the effect of hydrogen distribution in a fixed bed on the activity and selectivity of Co/SiO2 (22.2 wt.% Co) Fischer-Tropsch (FT) catalysts. Hydrogen is introduced from 4 equally spaced axial locations and the flow rates are adjusted with 3 different strategies; the so-called decreasing, equal, and increasing flow strategies. Distribution of hydrogen results in different H-2/CO ratio along the reactor, which in turn controls the product selectivity. As compared to the co-feed strategy, the decreasing strategy suppressed methane selectivity by 20%, while enhancing C5+ selectivity by about 16% and increasing chain growth probability to a limited extent. The olefin to paraffin selectivity ratio also shows an improvement by a factor of 1.6-1.8, depending upon the type of strategy employed. The dependence of product selectivity on the operating conditions such as temperature, overall H-2/CO ratio, and feed residence time was also explored. (c) 2004 Elsevier B.V. All rights reserved.