In this study, a parametric investigation is carried out to estimate the hydrogen energy potential depending on the quantities of H2S in Black Sea deep waters. The required data for H2S in Black Sea deep waters are taken from the literature. For this investigation, the H2S concentration and water layer depth are taken into account, and 100% of conversion efficiency is assumed. Consequently, it is estimated that total hydrogen energy potential is approximately 270 million tons produced from 4.587 billion tons of H2S in Black Sea deep waters. Using this amount of hydrogen, it will be possible to produce 38.3 million TJ of thermal energy or 8.97 million GWh of electricity energy. Moreover, it is determined that total hydrogen potential in Black Sea deep waters is almost equal to 808 million tons of gasoline or 766 million tons of NG (natural gas) or 841 million tons of fuel oil or 851 million tons of natural petroleum. These values show that the hydrogen potential from hydrogen sulphur in Black Sea deep water will play an important role to supply energy demands of the regional countries. Thus, it can be said that hydrogen energy reserve in Black Sea is an important candidate for the future hydrogen energy systems. (c) 2006 International Association for Hydrogen Energy.