Oil prices have plunged so rapidly that financial markets are treating them less as an opportunity than a danger, like a falling knife.

Currency rates are gyrating, oil-producing countries like Russia, Venezuela and Iran are hurting, and sectors of the bond market are threatened.

But unless you’re directly involved in the commodity markets, you may not be following the futures price of a barrel of oil. What hits home, especially if you drive a car with an internal combustion engine, is the price of gasoline: It has become spectacularly cheap.  Read more