<prompt> The best fuel gas when used with oxygen is:HydrogenNatural gasPropaneAcetylene  <response>: PropaneOf the fuel gases, the best choice is propane. Butane, which is more readily available in some parts of the world, has a similar flame temperature and heat content as propane. Both propane and butane have the advantage of being relatively pure compounds; therefore, they are uniform in quality are virtually water-free, and burn cleanly provided that the torch flame is properly adjusted. 