"Currently the United States is not running short of oil. In fact, the oil storage facility in Cushing, Okla., that supplies the nation’s heartland has record inventories because of expanding production in North Dakota and a new pipeline shipping increased supplies of synthetic fuel from oil sand fields in western Canada.
But the loss of more than a million barrels of sweet crude on world markets resulting from the turbulence in Libya is tightening supplies for European refineries that need high-quality oil to produce diesel fuel, which is popular in Europe.
By releasing sweet, or low-sulfur, crude oil from the reserve, Washington might relieve a bidding competition between American and European refiners for sweet crudes produced by Algeria and Nigeria, two producers that are straining to fill the gap left by Libya.
Saudi Arabia holds most of OPEC’s spare capacity, but its crude is mostly sour — that is, higher in sulfur content — and cannot easily replace the lost Libyan sweet crude."
http://www.nytimes.com/2011/03/04/business/energy-environment/04oil.html