Global oil prices have hit 40 U.S. dollars per barrel, the highest level in 13 years since Iraq invaded Kuwait ahead of the 1991 Gulf War.

New York's reference light sweet crude for June delivery climbed one dollar and 13 cents to 40.06 dollars Tuesday. The price of benchmark Brent North Sea crude oil also rose to close at 37.40 dollars in late afternoon trading.

The overnight rally stems from escalating concerns in that Saudi Arabia