Can you link one? A quick look gave this:

A recent study by the USGS estimates that there could be millions of Mt of natural hydrogen in accumulations in the Earth’s crust (Ellis and Gelman, 2024). However, there is a great deal of uncertainty associated with this prediction and the model does not evaluate the potential size or distribution of hydrogen accumulations. Most of this hydrogen is likely to be in accumulations that are too deep, too far offshore, or too small to ever be economically recovered. That said, even a small fraction of the estimated amount of subsurface hydrogen could potentially meet all global projected demand for hundreds of years. Consequently, the key to understanding geologic hydrogen resource potential is to examine the geologic factors that affect the potential to form accumulations.