The combination of theoretical calculations and laser flash photolysis experiments has aided in understanding the reactivity and properties of oxenium ions. Direct observation of the reactivity, spin configurations, and lifetimes of short-lived oxenium ions via laser flash photolysis (LFP) techniques is now possible due to the discovery of new photoprecursors to these species. These new precursors allowed the direct observation of the parent phenyloxenium ion in solution by using protonated hydroxylamine tetrafluoroborate salt. Computations suggest that the singlet-triplet gap (ΔEST) of aryloxenium ions can be tuned by substituents, and predicted a ground state triplet oxenium ion, which was confirmed by experimental studies. The interplay of theory and experiment in understanding these species is discussed.