Forget sophisticated economic models and swotting up on Iranian politics. Since 2003, there has been a much simpler way to guess the next year’s average oil price: add on another $10 or so per barrel.

Analysts’ current predictions for oil prices in 2007 span a wide range of $50-$70 a barrel (this year’s average price, so far, is $66). In December, however, oil industry executives surveyed by Deloitte struck a more bullish tone, with more than half saying the world economy could cope with oil at up to $90 a barrel.