Oil-producing countries will sell $240 billion of international assets this year, mostly stocks and bonds, in an attempt to hold together budgets blown apart by the slump in oil prices, according to estimates from JP Morgan. That sum will come from running down their foreign exchange reserves and Sovereign Wealth Fund holdings. They will also raise some $20 billion by selling government bonds of their own to help cover a current account shortfall of $260 billion, the U.S. bank predicts.

These countries will sell holdings of U.S. Treasuries and other bonds worth about $110 billion plus $75 billion of equity investments, up from $45 billion and $10 billion last year. The remaining funds will come from liquidating other assets such as cash, real estate and private equity.

"The lower the oil price, the higher the potential depletion of SWF assets as oil-producing countries struggle to prevent their spending from declining too much," JP Morgan strategists wrote in a client note.

"For 2016 we look for FX reserve depletion of $100 billion and a decline in SWF assets of $140 billion," they wrote, noting that asset sales last year, when plunging oil prices also left some countries with budget shortfalls, totalled $70 billion.

These estimates are based on the price of Brent crude oil averaging $31 a barrel this year, sharply down from $53 from last year, which would see producer countries' oil revenues plummet by $300 billion to $440 billion. Brent has tumbled 22 percent so far this month to a 12-year low of $27.67 thanks to a slowing demand growth and bumper supply. The slump has rocked global world markets and hit the finances and markets of oil producers especially hard.

Saudi Arabia's currency, the riyal, has fallen to a record low against the dollar on the forward market, while Russia's rouble has hit a record low and Gulf region stock markets are at multi-year troughs. Saudi Arabia, the world's largest oil exporter, could face a budget deficit approaching 20 percent of gross domestic product, according to some estimates.