On Sept. 11, 2007, the price of crude oil closed at $78.23 a barrel -- the last time oil closed below $79 a barrel, until Friday. What seemed like a bewildering ascent in the price of crude at the time is now a relief to traders, who watched oil fall $8.98 a barrel to close at $77.61 on the New York Mercantile Exchange, the lowest closing price in more than a year.

Like a number of other commodities, oil's move went from a steady ascent to a vertical bounce in the spring of 2008, topping out near $150 a barrel before speculative...