Fully correlated calculations using a multiconfiguration-self-consistent-field (MCSCF) treatment have been carried out to find the most stable structures of [O3H](+) and to improve on earlier calculations on the same system. The results are used to evaluate proton affinity (PA) and gas-phase basicity of the ozone molecule, quantities which can be compared with experimental data. The existence of regions of nonadiabatic coupling and of charge-exchange effects is evidenced and analyzed, with avoided crossings specifically located for one of the four most stable protonated adducts of ozone. The present study extends the level of accuracy achieved in earlier calculations on the possible structures for protonated ozone and gives specific suggestions on the microscopic processes for the formation of [O3H](+) in the gas phase.