The influence of solvent on the selectivity of alpha-olefin in the product hydrocarbon as a function of carbon number over a 20 wt.% Co on SiO2 catalyst under the typical reaction conditions of 513 K, 4.5 MPa and H-2/CO = 2 has been investigated. Hydrocarbons with different carbon numbers and molecular structures, including n-hexane, n-octane, n-decane, n-dodecane, n-hexadecane, iso-octane and decahydronaphthalene, were used as solvents. Although the selected solvents did not obviously affect the catalytic activity or chain growth probability (a-value), they exhibited remarkable influences on the alpha-olefin selectivity. In the case of n-hexane solvent, the alpha-olefin content in the product decreased markedly with increasing carbon number of the product. The n-decane solvent gave the highest olefin content. It was independent of carbon number on the C6+ product at the level of about 40%. This could be attributed to quicker desorption, diffusion and more suppressed re-adsorption of primary FTS product (alpha-olefin). (c) 2006 Elsevier B.V. All rights reserved.