Oil's four-year bull run to +$140 per barrel has increased the wealth of 'petrodollar' nations, and is about set to propel another shift, this time in the bond market.

Petroleum-exporting nations, such as Saudi Arabia and Russia are set to become the biggest creditor nations to the U.S. Government, Bloomberg News reported Monday.

Holdings of petrodollar nations increased 44% to $510 billion through April, Bloomberg News reported Monday -- an increase pace that's set to displace Japan, which holds the largest amount of U.S. Treasuries, at $592.2 billion.

Oil rose about 20 cents to $145.28 per barrel in late Monday afternoon trading.

When the typical investor speaks, Wall Street listens, to a degree. When Alan Greenspan speaks, Wall Street listens very closely.

Greenspan, who served as Chairman of the U.S. Federal Reserve for 18 years, said that while it's too soon to say a U.S. recession is up ahead, "the odds are clearly rising," National Public Radio reported. Greenspan added that U.S. economic growth is "getting close to stall speed."

Greenspan, 81, left the Fed in January 2006 after nearly two decades as leader of the world's most powerful central bank. When he left, the U.S. economy was growing at or near trend levels, or what economists call 'sustainable growth' levels.

However, the increase in subprime mortgage and related asset defaults, the housing sector's correction and persistently high energy prices, are expected to cool the current U.S. economic expansion, which began in 2001. Many economists expect Q4 2007 GDP growth to slow to 2.5-2.9%. Some are predicting an economic recession at the start of 2008. The U.S. economy grew at a 4.9% rate in Q3 2007.