Optimized structures for oxalate (C 2 O 4), malonate (O 2 CCH 2 CO 2), and succinate (O 2 C(CH 2) 2 CO 2) mono-and dianions are computed at the level of second-order Møller-Plesset perturbation theory (MP2). For oxalate, both anions exhibit D 2d and D 2h rotamers, and in addition, for the singly charged species, we find an anion-molecule complex of the form CO 2 -‚CO 2 . For the malonate and succinate anions we examine both keto and enol isomers; the keto structures are characterized by unhindered rotation of the CO 2 moieties about geometries of C 2 symmetry, while the enol isomers are much more rigid as a result of an intramolecular hydrogen bond. In both malonate and succinate, the enol isomer is the more stable form of the monoanion, while the keto isomer is the more stable dianion, although for O 2 CCH 2 CO 2 2-the estimated isomerization barrier is only about 7 kcal/mol. All of the dianions are adiabatically unbound and the enol dianions are vertically unbound as well. However, vertical detachment energies calculated by electron propagator methods at the partial third-order (P3) quasiparticle level with large, highly polarized basis sets suggest that the more stable keto forms of O 2 CCH 2 CO 2 2-and O 2 C(CH 2) 2 CO 2 2-are metastable, with vertical detachment barriers of about 0.2 and 0.6 eV, respectively. These results complement recent experimental observations of small dicarboxylate dianions in the gas phase.