Propane-fueled burners provide this to lift balloons; politicians make their own
They 
contain pressurized propane gas as fuel for the burners, but they... [DOC] [TLE] balloon flight | aviation | Britannica.com [PAR] Thus, the lifting force of a chosen gas at low altitudes can be obtained by ... 
Because the atmosphere is compressed by its own weight, it is less dense at 
higher ... the atmosphere is approximately two-thirds as dense and so will 
provide ... Hot-air balloon burners use vaporizing coils to preheat the fuel for 
efficient combustion.