A new hydrocarbon product distribution model for Fischer-Tropsch-synthesis (FTS) reaction has been developed. The model is based on the assumption that there are two types of active sites on the catalyst surface: type-1, where growth of hydrocarbon intermediates occurs, and type-2, where reversible readsorption of 1-olefins occurs. The readsorbed 1-olefins form alkyl intermediates, CnH2n+1, on the surface, which in turn can participate in several reactions: chain growth propagation, hydrogenation to n-paraffins, and dehydrogenation to 2-olefins. Chain growth is considered on the basis of methylene monomer (CH2) insertion mechanism. Steady-state mass balances for adsorbed intermediates C-1-C-50 and equations for the product formation rates were derived. The model has been tested using results from experiments conducted over long periods of time under industrially relevant conditions in a slurry reactor. The model predictions provide information on hydrocarbon product distribution, 2-olefin content and total olefin content as a function of carbon number. The curved line for the distribution of paraffins and olefins can be fitted well with the proposed hydrocarbon selectivity model, over the entire range (C-1-C-50) of carbon numbers. The kinetic model proposed in this paper can be used for interpretation of experimental data, comparison of performance of different catalysts, and reactor modelling and simulation studies.