We report multireference configuration interaction (CI), as well as coupled-cluster, calculations for the three O(P-3)H-2 potential-energy surfaces (two of A " symmetry and one of A' symmetry in C-s geometry) in the region relevant to the weakly bound O(P-3)... H-2 complex. The two electronically adiabatic states of A " symmetry correspond to an orthogonal transformation of two orthogonal electronic occupations of the O 2p orbitals. The transformation of the three electronically adiabatic states to an approximate diabatic representation, which involves four potential-energy functions, can be obtained, either from calculated matrix elements of the electronic orbital angular momentum or from analysis of the expansion coefficients of the CI wave functions. An exact treatment of the nuclear motion including spin-orbit coupling, based on the diabatic PES's (potential energy surfaces), is used to determine the energies of the lowest bend-stretch levels of complexes of O(3P) with both nuclear spin isomers of H-2 and D-2. The predicted dissociation energies (D-0) are 15.4 and 22.4 cm(-1) for the complexes with pH(2) and OH2, respectively, and 22.3 and 31.4 cm(-1) for the complexes with oD(2) and pD(2), respectively.