Paul, I assume you need a tank of hydrogen gas that is not depleted by something like 75% as hydrogen gas normally is when produced by electrolysis. With Linde AG (Leuna, Germany) we have a source of hydrogen gas that manufactures from natural gas. It's isotopic composition is at -220 per mill on the VSMOW scale. So, you should ask the hydrogen gas supplier whether the gas production is electrolysis or natural gas. Good luck. Willi -- ‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰ Willi A. Brand, Stable Isotope Laboratory [log in to unmask] Max-Planck-Institute for Biogeochemistry Tatzendpromenade 1a, 07745 Jena, Germany Tel +49-3641-643718 P.O.Box 100164, 07701 Jena, Germany Fax: +49-3641-643710 ‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰‰