"The savings could widen out to 20 cents to 25 cents per gallon this month," said OPIS analyst Tom Kloza. "The expanding gap should come as much cheaper wholesale prices work their way downstream and are compared with very steep increases that were characteristic of March 2012."
In 2012, almost every March day saw retail gasoline creep higher.
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Based on recent demand patterns, OPIS estimates that every penny of national savings on gasoline adds up to about $3.57 million per day.
"If U.S. gasoline prices move to say a 20 cent per-gal deficit to last year, there should be about $71.4 million more daily spending power for consumers after they take care of their fuel needs," Kloza said.
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So far the biggest year-over-year price drops have been in California, Indiana, Michigan, Oregon, and Washington. But gasoline prices in Colorado and North Dakota, for example, are still significantly more expensive than a year ago.
—By CNBC's Sharon Epperson; Follow her on Twitter: @sharon_epperson