Tuesdays are one of the better days to save on the price of gasoline but not the best day. Super America and some Holiday stations double coupon amounts on Tuesdays. And some sources claim that Tuesdays are, on average, the cheapest day of the week to purchase gasoline.

But many markets, including the Twin Cities, don't follow the national trend, said TwinCitiesGasPrices petroleum analyst Patrick DeHaan. We're more of a roller coaster market, he said. Our prices fall by a few pennies at a time and then go up like a shot. We may hate when prices shoot up, but the Twin Cities is one of the cheaper metro areas for gas prices, on average, said DeHaan.

Mondays mornings are the best time. Prices rarely go up on the weekend, so if you fill up before 9 or 10 a.m., you'll beat any price increases that day. After Monday morning, the best days to buy, in order, are Friday and then Tuesday.

Wednesday and Thursday often see price increases because the Department of Energy releases new petroleum status reports on Wednesdays.

Price hikes on Saturday and Sunday are not unheard of but rare.

The best way to track the cheapest gas prices in the Twin Cities is to use a tracker site such as Gas Buddy or Twin Cities Gas Prices. You can also follow their alerts to price increases on Facebook or Twitter.

The cheapest cities to buy gas in the Twin Cities metro, according to DeHaan, are Burnsville, Shakopee, Prior Lake, Shakopee, Coon Rapids and Woodbury. If you're passing through one of those areas soon, you might want to fill up while you're there.

Need a coupon now for a Tuesday? Here's one from Holiday's site for 5 cents off a gallon up to 15 gallons. You can also sign up to get additional Holiday offers sent via email.