The ruble hit a seven-month low on Monday, along with a number of other ex-Soviet bloc countries, including Belarus and Ukraine, and most of the oil exporters mentioned above. The collapse was inspired by turmoil in China, which is a crucial driver of global demand for commodities. (It's also worth pointing out that all commodities-based economies are hurt by an economic slowdown in major commodity consumer China, and so it should be expected that their currencies may suffer as well.)
According to calculations by Reuters, the implied demand for oil in China was 10.12 million barrels per day in July, a 4 percent drop from June. Based on EIA figures for April, that demand accounts for about 13 percent of global production. Slowing global demand is expected to continue next year.
But slowing demand isn't the only issue. OPEC has increased pumping to three-year highs, and U.S. producers have continued drilling even as prices plummet, feeding into the global oversupply. American shale oil producers are partially to blame for that supply-side problem, while OPEC output tends to be stable on a year-to-year basis, U.S. production has thrown a wrench into the works with its sudden, explosive growth.
OPEC leaders have criticized U.S. producers' "all-out exploitation of tight oil," and the Americans' expectation that OPEC countries will be willing to sacrifice market share in order to keep prices at reasonable levels.