Alkaline sodium borohydride solutions are potential hydrogen sources for fuel cells. Thermal properties of the NaBH4-NaOH-H2O ternary system were measured by DSC and temperature-rise calorimetry. Liquidus temperatures showed that it is possible to store and use the solutions well below 0 degrees C if NaOH concentration is less than 20wt%. The solubility of sodium borohydride was found to be large in these solutions, but decreased with increasing NaOH concentration. The optimum composition for alkaline borohydride solutions seems to be 15wt% NaBH4 in 10wt% NaOH considering both the liquidus temperature and hydrogen storage density. (C) 2008 Elsevier B.V. All rights reserved.