Catalyst activity and product selectivity studies of the conversion of synthesis gas to various hydrocarbon fractions were performed in a single-tube tube-wall reactor (TWR) using a Co-Fe plasma-sprayed catalyst with the operating conditions: temperature 250-275 degrees C, pressure 0.1-1.03 MPa, exposure velocity 139-722 mu m s(-1), and a H-2:CO ratio of 2.0. The catalyst activity in terms of CO conversion was highest (98.5% m/m) at an exposure velocity of 139 mu m s(-1), temperature of 275 degrees C, and in the pressure range 0.69-1.03 MPa. The selectivity to hydrocarbons was 43-50% (m/m) in the pressure range 0.69-1.03 MPa whereas the selectivity to C-5 + hydrocarbons was over 40% of the total hydrocarbons produced. The production of propylene was higher than ethylene under similar process conditions. The performance of the TWR was predicted by a numerical model. The model is based on the complete two-dimensional transport equations and reaction rate equations, developed for the Co-Fe catalyst. Predictions are made for the temperature along the axis of the reactor, for CO and H-2 conversions as functions of the reactor length and the exposure velocity, and the axial H2O and CO2 concentrations.