Ammonia borane (AB) is a promising hydrogen storage material as it contains 19.6 wt % hydrogen. In this article, our recently developed hydrothermolysis approach to release hydrogen is studied over a wide range of AB concentrations (6-88 wt %), at pressure 14.7 and 200 psia, and temperature 85-135 degrees C. It is shown that with increasing AB concentration up to 77 wt %, the H-2 yield increases, and that the role of thermolysis, when compared with hydrolysis, increases. The maximum hydrogen storage capacity, obtained at 77 wt % AB and T-reactor similar to 85 degrees C along with rapid kinetics, was 11.6 and 14.3 wt % at pressure 14.7 and 200 psia, respectively. To our knowledge, on a material basis, the AB hydrothermolysis process is the first one to provide such high hydrogen yield values at near PEM fuel cell operating temperatures without use of catalyst, and thus is promising for use in fuel cell-based vehicle applications. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 259-264, 2011