High quality global journalism requires investment. Please share this article with others using the link below, do not cut & paste the article. See our Ts&Cs and Copyright Policy for more detail. Email ftsales.support@ft.com to buy additional rights. http://www.ft.com/cms/s/0/8d57f5ec-6f38-11e4-b060-00144feabdc0.html#ixzz3JVgvMmo3 When US petrol prices halved in the autumn of 2008 it was the most timely and effective consumer stimulus of the whole financial crisis. Now the price of filling up a car is dropping again, but the US oil industry has changed so much, the effects are not quite as clear-cut. The shale oil revolution means that the US is no longer just the world’s top oil consumer – and thus a beneficiary of falling prices – but the top producer as well. Now when West Texas Intermediate falls from $95 to $75 a barrel, as it did during the past few months, economists have to factor in the hit to producers.