Oil futures hit $100 a barrel

Crude prices, which have flirted with $100 for months, have risen in recent days on supply concerns exacerbated by Turkish attacks on Kurdish rebels in northern Iraq and falling domestic inventories. However, post-holiday trading volumes were about 50 percent of normal Wednesday, meaning the price move was likely exaggerated by speculative buying.

"I would imagine the speculators are the biggest drivers today," said Phil Flynn, an analyst at Alaron Trading Corp., in Chicago.

It's hard to say whether prices would have risen as quickly on a normal trading day, Flynn said. While oil has soared on mounting supply concerns in recent months, speculators have often been cited as a reason for the swiftness of oil's climb.

Moreover, many of the concerns about supply disruptions have yet to materialize, but that hasn't stopped buyers from driving prices higher.

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