The H + O-2 --> O-2 + OH chain-branching reaction, one of the most important elementary reactions in combustion chemistry, represents a challenging benchmark system for testing dynamical theories against experiments. The translational energy dependence of the total reaction cross section of the H + O-2 (vibrational quantum number nu = 0) reaction was investigated experimentally employing a pulsed laser pump-probe technique and theoretically by means of quantum mechanical scattering calculations. The present results indicate that there is no sharp increase in reactivity for translational energies E-tr greater than or equal to 1.4 eV as was suggested by earlier experiments and approximate dynamical calculations. Furthermore, our results indicate that the potential energy surface needs to be improved to achieve quantitative agreement between experiment and theory.