Over the last year, foreign exchange traders have had an easy way to check up on oil prices. They simply look at how the euro is performing against the dollar. If the euro is gaining, then the crude price is rising.

That is what has happened most of the time. Crude has shot to a record while the euro has reached highs against the dollar – and the many macro hedge fund managers who have made this bet have done very well. But the last week suggests that relationship is weakening.