Most of this hydrogen is likely to be “in accumulations that are too deep, too far offshore, or too small to be economically recovered”, the study’s authors, USGS geologists Geoffrey Ellis and Sarah Gelman, wrote. However, if just 2% of this white hydrogen was recoverable, it could meet projected global hydrogen demand for around 200 years, they found. It would also, they added, contain roughly twice as much energy as is stored in all the proven natural gas reserves on Earth.