Actually it is not used as a liquid. It is STORED as a liquid and burned as a vapour. When the cylinder is sitting there you have static liquid with a vapour space above it. When the appliance is turned on, you are drawing off vapour and burning that. This reduces the pressure in the cylinder and the liquid begins to boil to replace the vapour. As the propane changes state from a liquid to a vapour it expands 277 times. That is how we get such a long amount of burn time from a relatively small container