For most of the past two decades, the world has enjoyed exceptionally low and stable energy prices, but for the past couple of years or so, world oil markets have been on an unnerving roller-coaster ride: prices collapsed to around $10 a barrel two years ago, and soared to a ten-year high of over $35 last year. It was those peaks that set off a political crisis over petrol prices and shortages in America's mid-western states last summer, and that provoked the fuel riots which paralysed several European countries in September. Now oil prices are lower, but remain volatile.
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