Actually, you're a stupid AC so it is understandable that you would just spout such nonsense, but H2 certainly does use proportionally more O2 that hydrocarbons when burnt. But that wasn't even my point. Supposedly we are close to being out of hydrocarbons (or so the eko-kooks would have us believe), so I'm not too concerned that burning the little left could deplete our oxygen. On the other hand, if someone has found a "vast" reserve of hydrogen and can tap it as a fuel source, then we are likely to focus less on renewable sources and just use that. And as we do there will be less and less free oxygen, particularly since we seem to use energy at rates faster than the planet restores oxygen by photosynthesis (otherwise there would be no "greenhouse gas" problem).