Ab initio electronic structure calculations are reported for OPO, its ions OPO+ and OPO-. Geometric parameters and rotational constants are calculated using the singles and doubles coupled cluster method, including a perturbational correction for connected triple excitations, CCSD(T), together with systematic sequences of correlation consistent basis sets. Energetic and structural properties of the OPO cation are reported for the first time. The 0 K adiabatic ionization potential and electron affinity are predicted to be 247.5+/-1 kcal mol-1 and 79.2+/-1 kcal mol-1, respectively.