A systematic study of the ozone potential energy surface was performed by means of high level ab initio techniques. The methods include icMR-CISD and icMR-AQCC with all electrons correlated using a full valence CAS reference space and basis sets up to sextuple-ζ quality along with extrapolation to the complete basis set limit. We computed a dense 3D grid as well as 1D cuts along stretching and bending coordinates around the open (C(2v)) equilibrium structure as well as along the minimum energy path to dissociation including the transition state and the van der Waals minimum region. The detailed analysis of our results confirms earlier calculations by the Schinke group and assures that these are not biased by deficiencies of the basis set, lack of relativistic corrections, or core correlation effects. Finally, we discuss possible sources of error that may explain the remaining discrepancies compared to experimental findings.