Electron correlation has been studied in the singly ionized 5p −1 , 5s −1 and 4d −1 states and the double ionized (5s, 5p, valence) −2 states of Ba by carrying out extensive configuration interaction Hartree-Fock calculations including the mixing of configurations with outermost valence electrons (nl = 6s, 5d, 6p, 4f, . . .). The results of calculations have been compared with existing experimental photoelectron, ion-yield, electron-ion coincidence, and Auger electron spectra.