A 10% change in the oil price is associated with around a 0.2% change in global GDP, says Tom Helbling of the IMF. A price fall normally boosts GDP by shifting resources from producers to consumers, who are more likely to spend their gains than wealthy sheikhdoms. If increased supply is the driving force, the effect is likely to be bigger—as in America, where shale gas drove prices down relative to Europe and, says the IMF, boosted manufactured exports by 6% compared with the rest of the world. But if it reflects weak demand, consumers may save the windfall.