BSR in shallow environments and TSR in deep reservoirs are key processes in the oceanic sulfur cycle.  Approximately, 10% (of the total gas) of H2S is produced in BSR settings, whereas 90% of the H2S is produced in TSR settings. If there is more than a few percent of H2S in any deep reservoir, then it is assumed that TSR has taken over. This is due to the fact that thermal cracking of hydrocarbons doesn't provide more than a couple percent of H2S. The amount of H2S is affected by several factors such as, the availability of organic reactants and sulfate and the presence/availability of base and transition metals.