Propane and butane are both members of the liquid petroleum gas family. They are similar and in some cases can be used for the same application, with minimal equipment modifications. There is a difference in the chemical make up of each fuel. For example, propane (C3H4) has a boiling point of –44 ° F, with 91690 BTU ‘s per gallon, and an octane number over 100. Butane (C4H10) on the other hand has a boiling point of 32° F, with 102032 BTU ‘s per gallon, and an octane number of 92.