Natural resource companies with global operations have no shortage of business challenges to deal with—supply and demand trends, political instability, regulatory hurdles, remote and dangerous working conditions, inadequate infrastructure and much, much more.

And even if they have managed all of these factors, there’s another variable that can have a huge impact on their success and yet is completely out of their control.

It’s the value of the U.S. dollar.

Commodities are bought and sold in dollars, so if you are a Russian manufacturer seeking to buy 1,000 metric tons of copper from Peru, you first have to get your hands on enough dollars to do the deal.

If the dollar strengthens against the Russian ruble, that 1,000 tons of copper will cost the manufacturer more because it will take more rubles to buy each dollar. Likewise, if the dollar weakens, the copper will be cheaper for the manufacturer because it will take fewer rubles to buy each dollar.

For the miners, a weak dollar is good because it stimulates demand for their output, but a strong dollar can also produce a benefit.

The chart above from PriceWaterhouseCoopers shows how the currencies of five key natural resources producing nations performed compared to the dollar in 2008.

The dollar gained value against all five to varying degrees—more than 40 percent against the South African rand, between 30 and 40 percent against the Chilean peso, Brazilian real and Australian dollar, and more than 20 percent against the Canadian dollar.

A strengthening dollar can help miners whose operating costs are in non-dollar currencies. These companies are paid for their production in appreciating dollars, while paying their labor, suppliers and other operating costs in depreciating currencies.

This explains in part why South African gold miners performed much better than their peers in late 2008—the rand depreciated 28 percent against the dollar in the fourth quarter alone. This lowered operating costs and improved relative profitability.