Mechanisms for the generation of hydrocarbon and oxygenate products from synthesis gas using the Fischer-Tropsch synthesis are presented. The data generated to date indicate that, while there are similarities between iron and cobalt catalytic synthesis mechanisms, the details differ. For the iron catalyst, it is concluded that an oxygenate mechanism is more appropriate in light of today's data. While less mechanistic data for the cobalt catalyst are available, it appears that a surface carbide mechanism is a better choice.