Results from alkene co-feeding and benzene poisoning experiments indicate that readsorption and secondary reaction of initially produced alkenes is an important pathway leading to the formation of long-chain hydrocarbons during Fischer-Tropsch synthesis. Synthesis sites are differentiated in short-chain and long-chain synthesis sites. Synthesis initiation by readsorbed alkenes on long-chain synthesis sites is favoured by increased reaction pressure and leads to the formation of predominantly long-chain hydrocarbons. When this type of synthesis becomes more pronounced, inflection points are observed in Anderson-Schulz-Flory plots of the product distribution. Secondary reactions are found to be very dependent on dynamic adsorption/desorption equilibria. An example of a mechanism which is consistent with the experimental observations is presented.