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Scott Jagow: No price is dropping faster than oil. Consider this: In July, the price of oil was $147 a barrel. This morning, it’s half that — $72. More from Ashley Milne-Tyte.

Ashley Milne-Tyte: Consumers and businesses started to cut back on their use of oil when prices shot up. It was then that demand began to weaken.

Daniel Yergin is author of The Prize: The epic quest for oil, money and power. He says even before the big run-up in crude prices, the economy was faltering. And now:

Daniel Yergin: The great global economic growth that propelled oil and other commodity prices up for five years is over.

But he says it’s not just global demand that influences oil prices:

Yergin: You know, the financial markets have come to be a very important part of the oil markets. And as hedge funds liquidate their positions, as they stop trading commodities, that is clearly one of the factors in the oil price.

Some blamed speculators for driving the price of oil to records. Yergin says many of those traders are less active, and others have disappeared from the market altogether.

In New York, I’m Ashley Milne-Tyte for Marketplace.