On the basis of recent detailed kinetics models, a multicomponent model for the Fischer-Tropsch synthesis in a stirred-tank slurry reactor is developed to interpret the essential bulk effects that enhance the deviations of hydrocarbon product distribution from the standard Anderson-Schulz-Flory (ASF) model. It is found that the reactor model with kinetics excluding olefin readsorption and secondary reactions (ORSR) on the catalyst surface could not predict the correct trends observed in experiments, while that using the kinetics models including ORSR effects could well interpret these two deviations from the ASF distribution. The important notation pointed out is that ORSR is greatly enhanced by less volatility of heavier hydrocarbons in a multiphase reactor, which produces significant deviations from the ASF distribution in experiments, namely, the increasing chain growth factor and decreasing olefin-paraffin ratio with increasing carbon number. In addition, the experimentally proven fact that the addition of olefins in the feed could enhance the yields of hydrocarbons heavier than the added olefins is well interpreted by this simulation.