Structures of the superelectrophilic fluorooxonium dications FOH32+ and F2OH22+ were calculated at the QCISD(T)/6-311G** level. Proton affinities of their precursor monocationic species were estimated by using G2 theory. For comparison, the parent oxonium dication H4O2+ was also calculated at the same level. The O,O- and O,F-diprotonated HFO structures 2c and 2d, respectively, were found to be energy minima. However, the oxonium dication 2c is less stable than the oxonium-fluoronium dication 2d by 14.9 kcal/mol. On the other hand, O,O-diprotonated F2O 3c was found to be the only minimum for the analogous system. All of these superelectrophilic, dicationic species have substantial kinetic barriers for deprotonations. The possible existence of these dicationic species in either superacidic media or the gas phase is implicated from these studies. The O-17 and F-19 NMR chemical shifts of the mono- and dications were also computed by the GIAOMP2 method.