Normally a gas, but compressible into a liquid, propane is commonly used as a heat source for engines, barbecues and homes.
Propane is the by-product of two processes: natural gas processing and petroleum refining. The supply of propane is not easily altered due to an increase in demand because it's a derivative of other processes. In the Third World, propane is the fastest growing fuel source, especially in China and India.
Propane is the fuel used in hot air balloons as well as in semiconductor manufacture to deposit silicon carbide. Also in recent years, the use of propane being used in vehicles has increased.