Quasiclassical trajectory calculations and accurate quantum dynamical studies were carried out for the reaction of ground state oxygen atoms O(P-3) with hydrogen molecules (H-2). Two newly reported potential energy surfaces (PESs) for the lowest triplet electronic state of H2O((3)A"), with slightly different potential energy barriers and long-range van der Waals well depths, were used in the calculations. The quasiclassical trajectory calculations reveal that, for collisions near the threshold, the reaction O(P-3) + H-2 -> OH + H is very sensitive to the van der Waals region while the quantum dynamic results clearly show that the reaction mainly occurs through tunnelling. (c) 2005 Elsevier B.V. All rights reserved.