A fluid supply system is provided which includes a filling station operable to provide a fluid to a fuel storage vessel. The fluid supply system is operable in a first mode to provide a fluid in a liquid phase from the filling station to the storage vessel and is operable in a second mode to prevent the supply of the fluid to the storage vessel. The storage vessel is in fluid communication with the fluid supply system and is operable to receive the fluid in the liquid phase when the fluid supply system is in the first mode and discharge the fluid in a gaseous phase to the filling station. At least one sensor is in communication with the discharge passage and the fluid supply, and operates to cause the fluid supply to operate in the second mode in response to a detected pressure drop.