Lighter fluid is most commonly butane – an alkane with only four carbon atoms.  Butane and other alkanes, such as propane, are flammable and good for heating because they don’t emit smoke while burning.  However, butane is desirable in lighters as the spark from its flint and steel can only create a flame by igniting a gas. Butane is gaseous at temperatures over -0.5 C, but it can turn into a liquid in a slightly pressurized container, making it safer to store.