The modern world's excessive dependence on fossil fuels is often cited as a cause of pollution, wars, and looming energy shortages. For these reasons, plans to switch from total reliance on a fossil-fuel economy to one that includes the use of hydrogen as a renewable, clean fuel source are now beginning to take shape. Hybrid gasoline and hydrogen cars are already on the roads in the United States, In addition, California's ambitious Hydrogen Highway Project, consisting of ISO to 200 fueling stations for hydrogen fuel-cell powered vehicles, is slated to be completed by the end of the decade.    This would closely match the deadline facing America's Big Three automakers, which have been ordered by the federal government to create viable fuel-cell engines by 2008. Though the public and private sectors are still hesitant to drop large sums into research and development, citing the high cost of hydrogen fuel, several optimistic government forecasts see the price dropping to a competitive $1.50 per gallon by 2010.    Proponents of hydrogen-based projects often point to Iceland, which is already making a huge effort to push ahead. The world's first hydrogen fuelling station, located on the outskirts of the capital. Reykjavik, powers a small fleet of buses. The country is looking into developing a nonpolluting “hydrogen economy,” with the power required to produce hydrogen to be generated by its environmentally friendly hydroelectric and geothermal plants.    So what's to stand in the way of this new utopia?  Logistics is one of the main problems. Though hydrogen is one of the most abundant elements in the universe, there is very little free hydrogen floating around. Hydrogen can be extracted from ethanol or petroleum, but the most common method of isolating the gas is by electrolyzing water, whereby an electrical current separates the constituent hydrogen and oxygen atoms of water molecules. Hydrogen-based power is often touted as environmentally sound, since the only waste products produced are heat and pure water, but if the energy needed to separate hydrogen from water is derived from conventional petroleum or nuclear sources, net pollution will remain the same or even increase. 　Deriving energy from “clean” sources such as wind, water, or solar energy is an option, but these alterative sources are not yet sufficiently developed, nor are they likely to be in the near future. Furthermore, there is no guarantee that the atmosphere would be cleaner with hydrogen-powered vehicles, for tiny molecules of hydrogen could easily leak from microscopic holes in fuel tanks. Some scientists even argue that such releases could worsen global warming. For these reasons, even hydrogen's most enthusiastic proponents admit that the technology is more likely to see applications in large stationary power plants than in vehicles.   Time and technology will tell whether a hydrogen economy will turn out to be a panacea for our energy problems or, perhaps more plausibly, just wishful thinking. As national energy strategists recommend, for now it is better to pursue a balanced portfolio of research and development efforts and continue to explore alternatives that do not depend on hydrogen.