We present a combined experimental and theoretical investigation of alkali metal sulfate ion pairs and their doubly charged dimers in the gas phase: Na+SO42-, K+SO42-, (NaSO4)(2)(2-), (KSO4)(2)(2-), and NaK(SO4)(2)(2-). We produced these anions using an electrospray technique and measured their photoelectron spectra at three photon energies, 355, 266, and 193 nm. The photoelectron spectra of each anion exhibit two detachment features, which approximately correspond to detachment from the HOMO and HOMO-1 of the SO42- group perturbed by the cations. The electron binding energies of the dimer dianions are lower than those of the monomers because of the strong electron-electron repulsion in the dianions. We also observed the repulsive Coulomb barriers in the dianions and their effects on the photodetachment spectra. We used density functional theory and ab initio molecular orbital theory to obtain the geometric and electronic structure of the ion pairs. The calculated electron binding energies and orbital energy separations are in reasonable agreement with the experimental values. We found that the MSO4- ion pairs have C-3v symmetry with a C-2v structure slightly higher in energy. In the dimer dianions the two alkali metal cations bridge the two SO42-groups.