Our mechanism for the methanation reaction pathway (Govender et al., 2008) during the FischerTropsch synthesis at high-temperature reaction conditions (330 C, H-2/CO = 15 and 1.2 bar) is extended here to account for the formation of C2+ hydrocarbons. The C-2 and C-3 hydrocarbon transients derived from (CO)-C-13 SSITKA experiments were used to discriminate between three mechanistic models. It is shown that a mechanism with two surface intermediates for the C2+ hydrocarbons and with olefin readsorption directly to the corresponding paraffin surface intermediate describes the data the best. Parameter estimates for the rate constants describing the formation of the C-2 are reported. The optimal model is also shown-to fit the C-3 hydrocarbons. The SSITKA measurements were also used to determine surface coverages and the turnover frequency. We propose C-s and C5H as the active C-1 species with both participating in chain initiation to form reactive C-2 species such as CsCsH. (c) 2014 Elsevier Inc. All rights reserved.