All syntheses start from the perxenates, which are accessible from the xenates through two methods. One is the disproportionation of xenates to perxenates and xenon:
: 2  + 2 OH →  + Xe + O + 2 HO
The other is oxidation of the xenates with ozone in basic solution:
:  + O + 3 OH →  + O + 2 HO
Barium perxenate is reacted with sulfuric acid and the unstable perxenic acid is dehydrated to give xenon tetroxide:
Any excess perxenic acid slowly undergoes a decomposition reaction to xenic acid and oxygen: