This is variant of Sulphuric Acid and less corrosive in nature than Sulphuric Acid. In general Oleum is assessed according to the free SO3 content by mass. It can also be expressed as a percentage of sulfuric acid strength and commonly this is 123% of Sulphuric Acid.
The main use of Oleum is in T N T (explosives) and also for manufacture of water based resins. Oleum is an important intermediate in the manufacture of sulfuric acid due to its high enthalpy of hydrogen. This also supplied in tankers load.
Uses of Oleum –