Thermal oligomerization is a radical based conversion process. It offers specific advantages to linear olefinic feed with a high alpha-olefin content, like primary Fischer-Tropsch products. Thermal oligomerization of C-4-C-14 Fischer-Tropsch feed materials has been investigated over the temperature range 320-400 degrees C. Motor gasoline, distillate, and lubricating oil quality was determined by the feed used, and operating conditions had only a minor influence. Good quality distillate (cetane >= 54) and lubricating oil (viscosity index of 100) could be produced, while the naphtha was suitable for chemical applications, like plasticizer alcohols production. Oxygenates present in the Fischer-Tropsch product had little influence on the process. Carbon formation was about 400 mu g center dot g(-1). Prospects for commercial application was discussed and is limited to an olefin-rich refining environment, where feed-specific advantages can be used to offset the disadvantage of a slow reaction rate (0.1 mol center dot s(-l).m(-3)).