A process for the conversion of synthesis gas to higher hydrocarbons by synthesis gas, at an elevated temperature and pressure, with a suspension of a particulate Fischer-Tropsch catalyst, in a system comprising at least one high shear mixing zone and a reactor vessel wherein the process comprises: (a) passing the suspension and the gaseous stream through the high shear mixing zone wherein the gaseous stream is broken down into gas bubbles and/or irregularly shaped gas voids; (b) discharging suspension having gas bubbles and/or irregularly shaped gas voids dispersed therein from the high shear mixing zone into the reactor vessel; and (c) maintaining the temperature of the suspension discharged into the reactor vessel at the desired reaction temperature by means of an internal heat exchanger positioned within the suspension in the reactor vessel. At least 5% of the exothermic heat of reaction is removed from the system by means of the internal heat exchanger. The remainder of the exothermic heat of reaction may be removed from the system by means of an external heat exchanger and/or through the introduction of a liquid coolant.