Oil prices have doubled from $50 a barrel in January 2007
Violence in Nigeria, Algeria and Pakistan, the weak US dollar and the threat of cold weather have all raised prices after the new year break.
Light sweet crude rose $4.02 to $100 a barrel in New York, prompting a drop in shares and a surge in gold prices.
There are concerns that the high price of oil will stoke inflation at a time when many central banks are trying to cut interest rates to stimulate growth.
US shares had already been hit on Wednesday by figures showing that the manufacturing sector was contracting.
After oil broke the $100 barrel they fell further, with the Dow Jones closing down 1.7% or 220.9 points at 13044.0.
"All of the factors that pushed us above $80 are now moving us higher," said Peter Beutel at Cameron Hanover in Connecticut.
"Until we get more supply or demand starts to take a hit, there is no reason we can't see any number."
Low volumes
But some analysts played down the relevance of passing the $100 mark.
"The entire focus on $100 oil is frivolous," said Tim Evans at Citigroup Futures Research in New York.
"It is not a magic number. It doesn't suddenly make this a fundamentally strong market."
Trading volumes were about half of their usual levels as traders returned from their new year breaks, which may have exaggerated the effect of speculative transactions, analysts said.
"I would imagine the speculators are the biggest drivers today," said Phil Flynn from Alaron Trading in Chicago.
$100 is just the beginning
Zachary Oxman, Wisdom Financial
The oil-producers' cartel Opec has also blamed speculators for the high price of crude and said that there is plenty of the fuel in the market to meet demand.
President Bush has said he would not be drawing on the US Strategic Petroleum Reserve (SPR) to try to bring down prices.
"This president will not use the SPR to manipulate (oil prices)," White House spokeswoman Dana Perino said.
"Doing a temporary release of the SPR is not going to change prices very much."
Moving on up?
There are those who believe that oil prices can rise significantly higher.
While daily price rises have been blamed on unrest in oil-supplying countries such as Nigeria, an underlying and significant factor has been an increase in demand from China and India.
"$100 is just the beginning," said Zachary Oxman, senior trader at Wisdom Financial in California.
"This is kicking off what you are going to see this year. There will be huge moves up in gold and huge moves up in crude."
Central banks such as the Bank of England and the Federal Reserve are worried that rising oil prices will prevent them cutting interest rates.
Expensive oil increases inflation, which makes it more difficult to make the rate cuts that the central banks may have to implement to boost growth.
El barril de petróleo llegó a comerciarse en más de 100 dólares, un precio impulsado por la fuerte caída del dólar, la tensión en países como Nigeria y Pakistán, y una gran especulación. El "light sweet crude" tuvo un alza de $3,66 – a 99,64 dólares – poco después de llegar a cotizar en más de $100 en el NYMEX (New York Mercantile Exchange).

El crudo ligero dulce había aumentado $4,02 a $100, provocando una caída en la acciones y un aumento en el precio del oro. En Londres, el Brent también rompió un umbral tras cerrar en $97,71, con un alza de $3,89.

El aumento en la violencia en Nigeria, junto con la gran tensión vivida en Pakistán tras el asesinato de la ex Primera Ministra Benazir Bhutto, estimuló el precio del petróleo, cuyo último récord databa del 21 de noviembre y llegaba hasta $99,29 por barril.

Se teme que el alto precio del petróleo cause inflación, al mismo tiempo que varios bancos centrales recortan sus tasas de interés para estimular el crecimiento. Las acciones estadounidenses fueron afectadas el miércoles luego de un reporte que indicaba que el sector de manufactura se había encogido, y recibió otro golpe con la fuerte subida del petróleo. El Dow Jones retrocedió 215,1 puntos, o 1,6%, llegando a un bajísimo 13.049,73

"Todos los factores que nos impulsaban arriba de $80 nos empujan más alto aún", dijo Peter Beutel en Cameron Hanover, en Connecticut. "Hasta que haya más oferta o la demanda baje, no hay razón por la cual no podamos ver ningún número."