The design and the performances of reactors for the low-temperature Fischer-Tropsch synthesis may be strongly affected by the presence of a liquid phase creating a boundary layer around the catalyst pellets and filling their pores. Accordingly, it is of the utmost importance to be able to compute the yield of liquid products formed during the reaction. In this paper, such a problem has been faced through the joint use of a detailed mechanistic kinetic model, able to predict the product yields as a function of the process conditions, and of a nonideal isothermal and isobaric vapor liquid equilibrium calculation. It has been found that when a representative cobalt-based catalyst is operated at the typical low-temperature Fischer-Tropsch synthesis process conditions, more than 99 mol % of the hydrocarbon products are in the vapor phase. In particular, C20- species are almost entirely vapor, C31+ species are almost entirely liquid, while C-21-C-30 species are split between the two phases. The precise prediction of the yield of each reaction product has been found a key-requirement to grant an accurate description of the phase equilibria within Fischer-Tropsch reactors.