Kinetic models for Fischer-Tropsch synthesis (FTS) were derived to express the reaction behavior in either conventional reaction media (gas-phase) or nonconventional media (near-critical and supercritical solvent media). These models we developed from experimental data generated from a commercial alumina supported cobalt catalyst (15% Co/Al2O3) in a fixed bed reactor. Two models were developed: the first one assumes ideal gas phase behavior for the gas phase reaction and uses partial pressures to express reactant and product concentrations in rate expressions while the second model accounts for the nonideal behavior of the reaction mixture under elevated pressures via the utilization of fugacity parameters and fugacity coefficients. The fugacity coefficients were estimated from a modified Redlich-Kwong-Soave equation of state. A comparison was conducted between the estimated kinetic parameters from the fugacity-based kinetic model and the partial pressure based kinetic model. The heat of adsorption of carbon monoxide and hydrogen was calculated from the estimated kinetic parameters and an attempt was made for qualitative analysis of mechanistic details of the reaction in both near critical and supercritical FTS and gas-phase FTS. It was observed that the fugacity-based models more accurately predict the carbon monoxide consumption rates in the gas phase as well as in near critical and supercritical FTS conditions. Similarly, the fugacity-based model was found to successfully predict the methane formation rates for both gas phase FTS and the near critical and supercritical phase FTS.