An ab initio potential energy surface for the triplet state of OH3+ has been constructed at the MP2/6-311G(2d,p) level of theory. Classical simulations of the title collisions have been carried out to evaluate the rate coefficients for three reactions, including H-3(+)+O --> H2O++H. Examination of the singlet-triplet energy gap across the triplet surface has shown no evidence for significant surface crossing effects on the dynamics.