The geometries, enthalpies of formation (ΔH° f ), separations of electronic states, electron affinities, gas-phase acidities, and bond dissociation energies associated with the alkali metal monoxide anions (MO - ), monoxide radicals (MO . ), and hydroxides (MOH) (M = Li, Na, and K) have been investigated using single-reference and multireference variants of the WnC procedures. Our best estimates of the ΔH° f values for the ground states at 298 K are as follows: 8.5 ( 3 π LiO - ), 48.5 ( 2 π LiO), -243.4 ( 1 σ + LiOH), 34.2 ( 3 π NaO - ), 86.4 ( 2 π NaO . ), -190.8 ( 1 σ + NaOH), 15.1 ( 1 σ + KO - ), 55.9 ( 2 σ + KO . ), and -227.0 ( 1 σ+ KOH) kJ mol -1 . While the LiO . and NaO . radicals have 2 π ground states, for KO . , the 2 π+ and 2 π electronic states lie very close in energy, with our best estimate being a preference for the 2 σ + state by 1.1 kJ mol -1 at 0 K. In a similar manner, the ground state for MO - changes from 3 π for LiO - and NaO - to 1 π + for KO - . The 1 σ + state of KO - is indicated by the calculated 1 diagnostic and the SCF contribution to the total atomization energy to have a significant degree of multireference character. This leads to a difference of more than 100 kJ mol -1 between the single-reference W2C and multireference W2C-CAS-ACPF and W2C-CAS-AQCC estimates for the 1 σ + δH° f for KO - .