Shale gas and eased sanctions on Iran will test Opec’s ability to curb output and buoy prices.
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At a private dinner early in November a group of executives from one of the world’s largest commodity traders was asked to predict the price of oil in a year’s time. Without exception the forecasts, scribbled on place cards without consultation, were for Brent crude to fall well below the $100 a barrel level it has traded above for most of the past three years.

Those predictions reflect a growing consensus in the oil market. From US shale to an easing of sanctions on Iran, the coming years are expected to provide a huge boost to global output, inverting the structure of the oil market in which supplies have long been rationed by a handful of producers.