If you needed a currency to act as a proxy for oil prices, your first port of call would probably be one of the main producing nations'.

However, your best bet now would in fact be a currency whose home nation barely squeaks into the top 30 national drillers and pumpers: the Australian dollar.

Recent research from Brown Brothers Harriman found that the Aussie had a 60-day correlation of 0.53 with oil, defined here as front-month West Texas Intermediate futures. That's not exactly eye-popping, but it is higher than anything the currencies of Canada, Norway, Russia, Mexico or Norway can boast, despite the fact that they all dwarf Australia in terms of crude output.

So, how to explain what looks like an odd correlation quirk? Well, it seems reasonable to suggest that the Australian dollar's position as the pre-eminent currency bet on global growth (lots of raw materials, strong links with China, etc...) allies it strongly with crude, the pre-eminent commodity bet on the same thing.

The Aussie's 60-day correlation with the S&P 500, for example, remains just about the highest of the lot, coming in at a near exact 0.91. Not only is this extremely high, it has remained so where other close equity links, such as the euro's, have faded.

Moreover, if you look at other oil producers' currencies, such as the Norwegian krone, it's not that hard to find a more persuasive influence over direction; its correlation with the euro, for example, is 0.92, which means the single currency, not oil, is driving there.

However, BBH's head of global currency strategy, Marc Chandler, says the relationship between oil and the Aussie is a subtle and complex thing; one of those correlations on which more work needs to be done.

Oil has a much weaker link to the S&P 500 than the Aussie does, for example, which you might not expect if 'growth' were the only support for the currency's relatively strong link to crude.