A substantial part of the runup in oil prices over the last few years is a function of the falling American dollar.
That sentence was spurred by a friend wondering why gas is cheaper now than it was last year, despite an increased price of oil - when stated in USD. Well, because the CAD has appreciated, just as most currencies have, relative to the USD.
Conclusion: Someone needs to index the oil price so that is abstracted from currency movements. Sadly, I do not have a reliable method to do this. Does such an index exist?