The potential energy surface of the HO+O double left right arrow HO(2)double left right arrowH+O-2 reaction system is characterized by ab initio calculations. The complex-forming bimolecular reaction is then treated by statistical rate theory, using statistical adiabatic channel and classical trajectory calculations for the HO+O double left right arrow HO2 and HO(2)double left right arrowH+O-2 association/dissociation processes. Specific rate constants k(E,J) of both reactions as well as thermal rate constants are calculated over wide ranges of conditions. Open shell quantum effects are important up to room temperature. The good agreement with experimental results suggests that the ab initio potential is of sufficient accuracy. There is no evidence for non-statistical effects or for a significant contribution from electronically excited states. The comparison with rate data for the H+O-2--> HO+O reaction, because of the remaining uncertainty in the heat of formation of HO, is somewhat inconclusive. Apart from this problem, the calculated rate constants appear reliable between 0 and 5000 K.