Oil hovered on the brink of $100 a barrel on Wednesday. Mixed data on US crude inventories did not quite push it over the threshold. But the world is having to accustom itself to the idea of a three-figure oil price. The implications for the health of the world economy are troubling.

“Until recently, there has been less concern about oil in the $90s than there was when it was $60 or $70. But it is obvious that oil at $100 is going to have much more impact than oil at $70,” said Daniel Yergin, chairman of Cambridge Energy Research Associates.