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The use of hydrogen fuel is another alternative under development in various countries, alongside, hydrogen vehicles though hydrogen is actually an energy storage medium, not a primary energy source, and consequently the use of a non-petroleum source would be required to extract the hydrogen for use. Though hydrogen is currently outperformed in terms of cost and efficiency by battery powered vehicles, there are applications where it would come in useful. Short haul ferries and very cold climates are two examples. Hydrogen fuel cells are about a third as efficient as batteries and double the efficiency of gasoline vehicles.