Method and reactor for performing Fischer-Tropsch (FT) synthesis with controlled steam partial pressure by introducing cool points in the FT reactor, typically in form of cooled solid surfaces. At the surface, the low temperature will force condensation of the water into a liquid film. Thereby, the partial pressure of steam in the gas and reactor will not exceed significantly the vapor partial pressure at the liquid film and water from the gas stream will be removed as it is produced, i.e. steam induced deactivation is avoided. In addition, the decrease of hydrogen and carbon monoxide partial pressures due to dilution by steam will be kept low ensuring a constant high reaction rate.