The effect of co-feeding nitrogen in Fischer-Tropsch synthesis (FTS) in a fixed bed reactor over a Co/TiO2 catalyst was investigated. The partial pressure of reactants (CO and H-2) in the feed to the reactor was kept constant, while the partial pressure of N-2 was switched between a low and high value. The low value corresponded to a syngas feed while the high value corresponded to a feed of syngas enriched with N-2. A comparison of the results obtained from more than four switches between syngas and syngas enriched with N-2 are reported. The results indicate that there was almost no effect on the overall reaction rate, but that there was a significant, positive effect on the product selectivity. A lower selectivity to the undesired light hydrocarbons (especially methane) was observed when co-feeding N-2. Such results cannot be explained by classic kinetics alone as the partial pressures of CO and H-2 were held constant during the experiment. The laboratory data indicates that the selectivity to the (C5-C19) fraction is particularly enhanced by co-feeding N-2 in FTS. (C) 2016 Elsevier B.V. All rights reserved.