After a generation on the sidelines, the US dollar has re-emerged as a central issue in the pricing of oil. Since the credit crunch in August, when the dollar has gone down, oil has gone up, by an average ratio of more than 5 to 1. Since August 21, the greenback has declined 4 per cent versus the euro; West Texas Intermediate crude, the global oil benchmark, meanwhile, is up 25 per cent.

Why are commodities traders fixated on the dollar? Like other oil market puzzles, the answer may lie in Saudi Arabia.