Oil prices vaulted to a record $100 a barrel on Wednesday as violence in Nigeria, tight energy stockpiles and a weaker dollar triggered a surge of speculative buying, dealers said.

Oil's climb to the psychologically key triple-digit price helped send stocks tumbling on Wall Street and further darkened an already gloomy economic outlook in the United States, which has been battered by a housing crisis and credit crunch.

"Oil hitting $100 a barrel has sparked some concerns about the consumer and inflation," said Todd Salamone, vice president of research at Schaeffer's Investment Research.

Charles Prince, the chairman and chief executive of one of the world's biggest banks, Citigroup, has resigned.

He will be replaced as chairman by former US Treasury Secretary Robert Rubin, while Sir Win Bischoff will serve as interim chief executive.

Investor calls for Mr Prince to go have increased since the bank reported a 57% drop in quarterly profits, after losses in the sub-prime mortgage market.

He is the second head of a leading US bank to step down within a week.

The head of Merrill Lynch, Stan O'Neal, resigned after reporting heavy losses.

Oil prices receded on Friday as dealers took profits from a record rally over $90 a barrel that was spurred on by winter supply worries and the weakening U.S. dollar.

U.S. crude settled down 87 cents at $88.60 a barrel, down from the all-time high of $90.07 hit earlier in the day. London Brent crude lost 81 cents $83.79.

U.S. oil has rallied more than 15 percent since October 8 as the dollar slipped to record lows against other currencies, fueling concerns about their effects on the economy of top consumer the United States.

Nasdaq has given potential suitors for its stake in the London Stock Exchange until Friday to state their interest, according to reports.

Nasdaq Stock Market has given potential bidders for its 31 percent stake in the London Stock Exchange until Friday to express interest in the stake, according to media reports Monday.

Nasdaq has asked for suitors to express interest by the end of the business day Friday, the Wall Street Journal reported, citing people familiar with the matter. The deadline isn't firm, the paper said. The stake is worth about $1.71 billion.