The plummeting price of oil could cause another source of capital to dry up: the Sovereign Wealth Funds (SWFs) of the Persian Gulf. This could be another blow for global credit markets, says Irwin Greenstein. These oil-rich funds fueled with petrodollars invested trillions over the past few years, notably with high-profile infusions of billions in CitiGroup, Carlyle Group, Merrill Lynch and the Nasdaq Stock Market.