Burning diesel in a power plant to create electricity, using that electricity to seperate hydrogen from ocygen in water, after that, using the Hydrogen to power the latest Honda STILL beats the energy converted by a normal car engine running on gasoline.
However, Hydrogen cars are no magic answers to the global energy requirement, - they are merely a sideshow. They can prolong the inevitable "run-out-of-oil" problem a bit, and of course, city traffic loaded with just Hydro cars would leave practically NO pollution. But eventually, mankind will either have to harness new energy sources, or change its habits drastically............