RCCSD(T) calculations, with an effective core potential for the inner electrons of potassium, and large polarized valence basis sets, have been used to calculate ionization energies of KO2, In addition, the binding energies of the ground electronic states of KO2, X-2 A(2), and KO2+, X(3)Sigma(-), have been determined. Comparison with previous values is made, where possible, and an estimate made of the errors in our calculations. The binding energy of KO2+ is found to be very limited. It is concluded that the role of KO2+ in the upper atmosphere will be small. (C) 2002 Elsevier Science B.V. All rights reserved.