The Fischer-Tropsch synthesis (FTS) in gaseous and supercritical phases was examined in a continuous, high-pressure fixed-bed reactor by employing a cobalt catalyst (Co-Ru/gamma-Al2O3). The kinetic modeling of the FTS was investigated in the reactor over a 60-80 mesh cobalt catalyst. The Langmuir-Hinshelwood kinetic equation was used for both the Fisher-Tropsch (FT) and water gas shift (WGS) reactions. The kinetic model was applied for simulation of the reactor with 16-20 mesh cobalt catalyst. The simulation results showed a good agreement with the experimental data. The experimental data showed that higher CO conversion and lower CH4 and CO2 selectivities were achieved in supercritical media compared to the gaseous phase. The BET surface area and pore volume enhancement results provided evidence of the higher in situ extraction and greater solubility of heavy hydrocarbons in supercritical media than in gaseous phases. Furthermore, the effects of supercritical solvent such as n-pentane, n-hexane, n-heptane and their mixtures were studied. Moreover, the influence of reaction temperature, H-2/CO ratio, W/F(CO+H2) and pressure tuning in the supercritical media FT synthesis were investigated, as well as the effect of the supercritical fluid on the heat transfer within the reactor. The product carbon distribution had a similar shape for all types of solvents and shifted to lighter molar mass compounds with increasing temperature, H-2/CO ratio, and W/F(CO+H2). Finally, the product distribution shifted to higher molar mass hydrocarbons with increasing pressure. As a result, one may conclude that a mixture of hydrocarbon products of the FTS can be used as a solvent for supercritical media in Fischer-Tropsch synthesis.