The price of a barrel of oil is at near 6 1/2-year lows this week as concern over China's plunging shares and the world's growth has shaken global markets.
Oil prices have been softening since the summer of 2014, recovering slightly this year before falling more than 5 percent on Monday. The decline is bad news for countries that rely on crude petroleum exports.
A sudden drop in prices can dramatically affect the currencies of those countries—most notably Russia, which produces about 12 percent of the world's crude oil supply. The country depends on sales of oil and natural gas for a more than 50 percent of its federal budget revenue, according to the Energy Information Administration. But the ruble is not the only currency that's moved by changing oil prices.