It's not hydrogen that's the limiting factor, it's the carbon. Carbon, like silicon (in rock), tends to bind to oxygen whenever possible. So long-chain hydrocar

It's not hydrogen that's the limiting factor, it's the carbon. Carbon, like silicon (in rock), tends to bind to oxygen whenever possible. So long-chain hydrocarbons would have to in highly anoxic regions. And there's also the issue of reacting with all that abundant hydrogen to form methane, although I'm not sure offhand which direction the binding energy difference favors on that one.