Reactions over olefins introduced during FT synthesis have been studied in a trickle bed reactor. Incorporation of 1-olefins into a growing alkyl chain could remarkably enhance the selectivity up to around 90% in heavy wax or middle distillate from syngas and could decrease the yields of lighter hydrocarbons with a higher CO conversion compared to the conventional FT synthesis. Results showed two significant processes the degradation of 1-olefins with successive demethylation, and its chain growth with incorporation by methylene species formed from demethylation, which is defined as the disproportionate reaction. The disproportionate reaction is competitive with introduced 1-olefins incorporating CH2 species formed from syngas into heavier hydrocarbons and is effectively controllable; Such control strongly depends on the process conditions. In general, the elimination of diffusion limitations for introduced 1-olefins and operating conditions that give a high intrinsic chain growth probability (alpha value) are favorable for suppressing the disproportionate reaction and for promoting the chain growth by the incorporation of syngas-formed CH2 species to increase the yields of heavier FT products. (C) 2007 Elsevier B.V. All rights reserved.