A fuel storage system (2, 5) comprising: a fuel tank configured to store a liquid fuel; a controllable pressure source for altering the pressure in an ullage space of the fuel tank; characterised by the fuel storage system further comprising a controller (24, 54) configured to: calculate a value for a temperature of fuel inside the fuel tank at a given time based on a current value of a temperature inside a different fuel tank using a predefined relationship between temperature of fuel in the different fuel tank and temperature of fuel in the fuel tank; determine a target pressure for the ullage space at the given time based on information relating to the temperature of fuel inside the fuel tank at the given time, wherein the information relating to the temperature of fuel inside the fuel tank at the given time comprises a current measured value of a parameter indicative of the temperature of fuel inside the fuel tank, and wherein the parameter indicative of the temperature of fuel inside the fuel tank is the temperature of fuel inside the different fuel tank; and control the pressure source such as to cause the pressure in the ullage space to be substantially equal to the target pressure. a fuel tank configured to store a liquid fuel; a controllable pressure source for altering the pressure in an ullage space of the fuel tank; characterised by the fuel storage system further comprising a controller (24, 54) configured to: calculate a value for a temperature of fuel inside the fuel tank at a given time based on a current value of a temperature inside a different fuel tank using a predefined relationship between temperature of fuel in the different fuel tank and temperature of fuel in the fuel tank; determine a target pressure for the ullage space at the given time based on information relating to the temperature of fuel inside the fuel tank at the given time, wherein the information relating to the temperature of fuel inside the fuel tank at the given time comprises a current measured value of a parameter indicative of the temperature of fuel inside the fuel tank, and wherein the parameter indicative of the temperature of fuel inside the fuel tank is the temperature of fuel inside the different fuel tank; and control the pressure source such as to cause the pressure in the ullage space to be substantially equal to the target pressure. calculate a value for a temperature of fuel inside the fuel tank at a given time based on a current value of a temperature inside a different fuel tank using a predefined relationship between temperature of fuel in the different fuel tank and temperature of fuel in the fuel tank; determine a target pressure for the ullage space at the given time based on information relating to the temperature of fuel inside the fuel tank at the given time, wherein the information relating to the temperature of fuel inside the fuel tank at the given time comprises a current measured value of a parameter indicative of the temperature of fuel inside the fuel tank, and wherein the parameter indicative of the temperature of fuel inside the fuel tank is the temperature of fuel inside the different fuel tank; and control the pressure source such as to cause the pressure in the ullage space to be substantially equal to the target pressure.