Operating conditions aﬀect the Fischer-Tropsch reaction and selectivity of product, while also depending on the catalyst composition and reactor type. By designing experimental methods, the modeling of hydrocarbon selectivity and CO conversion of the Fischer Tropsch synthesis over Co-based catalyst on a SiO2 support has been investigated in this study. The variable parameters for modeling consisted of a total pressure between 10 and 25bar, temperature range of 503–543K, and space velocity range of 1800–3600. The response surface methodology was applied to study the eﬀects of temperature, pressure, space velocity, and their interactions on CO consumption rate, and the selectivity of methane, C5+, CO 2, and hydrocarbons.A comparison of the models showed that CO conversion increased with an increase in both temperature and pressure. gas-to-liquid synthetic fuelalsoshowslowemissionsofcarbonmonoxide itcanbeconsideredasacleanfuel.Theselectivityequationof methane indicates that temperature has the maximum eﬀect on production; with an increase in temperature an increase in methane value occurs. For each product, the selectivity model was obtained and the optimal conditions were determined according to whether the materials were desirable or undesirable.