Geometry optimization and harmonic vibrational frequency calculations at the CASSCF, CISD, UMP2, QCISD, CCSD(T), and B3LYP levels of theory were performed on the ground (X) over tilde(2)A(2) state of KO2. Various augmented effective core potential and all-electron basis sets were employed, with the largest being the LANL2DZ effective core potential augmented by [6s6p3d1f], the all-electron basis set, [11s10p5d3f] for potassium, and aug-cc-pVTZ for oxygen. These calculations lead to tile conclusion that the C-2v (X) over tilde(2)A(2) state of KO2 has an equilibrium bond angle of 32.3 +/- 0.5 degrees, a K-O bond length of 2,410 +/- 0.005 Angstrom, and an O-O bond length of 1.341 +/- 0.001 Angstrom. The B3LYP density functional method is also employed for NaO2 and LiO2, and it appears that this method does not suffer from symmetry breaking; a similar conclusion is reached for the QCISD) method. Isotopic shifts for all three molecules are also reported and compared to available experimental values.