Oil prices have soared by more than a third since August.
A stand-off between Turkey and Kurdish PKK fighters, the weakening US dollar, easing interest rates and winter supply fears have provoked a fresh wave of investment capital.$100 dollar mark
The US Federal Reserve Federal Open Market Committee meets on October 30-31, and Wall Street is predicting another rate cut as the US housing downturn deepens.
Expectations of a cut have helped push the dollar to record lows against several currencies and boosted the price of dollar-denominated commodities.
Central banks also have poured billions of dollars into financial markets to help ease the credit crisis, and much of that money has been invested in energy, commodities and emerging markets.
Frances Hudson of Standard Life Investments said: "There's huge amount of speculation from hedge funds and others, they are all focused on the $100 barrel mark.
"If volatility decreases significantly, they'd stop playing."
Opec has ignored calls from importer nations to raise crude output.
Abdullah al-Attiyah, Qatar's oil minister, said: "I haven't any signal that there is any shortage of crude ... I believe a big portion of the oil price today is related to geopolitics and fear factors, and we cannot solve it."