Many consumers also have a few minutes to pop in for coffee or other convenience items that many stations sell for higher profit margins than gasoline. "If a one-penny drop at the pump brings 10% more people into the station, it's worth it," DeHaan says.

In states where stations offer the lowest prices during the workweek, the expert suspects quirky local traditions are at work.

"There's a blind rule that prices in Ohio, Michigan and Indiana are generally the best on Monday mornings at 10 a.m. because they're set at the corporate office -- and those guys don't decide what to do until they've come in at 9 a.m. and figured out what's going on [in the energy markets]," he says.

Here's a look at which days GasBuddy found generally offer the lowest pump prices in each of the 50 states and the District of Columbia. Although the best day for cheap prices varied from year to year in many states during the 2010-13 period GasBuddy studied, the days below reflect the best general advice about when to buy gas in each locale.

Monday: Indiana, Iowa, Kentucky

Monday or Saturday: Ohio, Oklahoma

Early week (Monday or Tuesday): Oregon

Tuesday or Thursday: Wyoming

Midweek (Tuesday through Thursday): Kansas, North Dakota, Utah

Wednesday: South Dakota

Thursday: Delaware, Maryland

Thursday or Sunday: New Jersey

Late week (Wednesday or Thursday, plus an occasional Friday or Saturday): Alaska, California, Montana, Nevada, New Hampshire

Weekends (Friday through Sunday, with a spillover into Monday in some cases): Alabama, Arizona, Arkansas, Colorado, Connecticut, District of Columbia, Florida, Georgia, Hawaii, Idaho, Illinois, Louisiana, Maine, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Nebraska, New Mexico, New York, North Carolina, Pennsylvania, Rhode Island, South Carolina, Tennessee, Texas, Vermont, Virginia, Washington State, West Virginia, Wisconsin

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