It's been a roller coaster year for gas prices, which began the year averaging $3.29 a gallon, then zoomed to $3.78 in February before dropping to $3.50 last month. Current average price: $3.60 nationally.

Troubles at several oil refineries are driving gasoline prices sharply higher in the Midwest, and the regional shortages are expected to boost pump prices nationwide.

Gas prices in Minnesota, North Dakota, South Dakota and Nebraska have spiked up to 27 cents a gallon the past week alone. Behind the rise: outages and extended maintenance has curbed output at refineries in Joliet, Ill., Whiting, Ind; Tulsa, Okla, and Eldorado, Kansas.

In Minnesota, regular, unleaded gas now averages $3.99 a gallon. That's an all-time state record.

With some Twin Cities outlets now selling gas for more than $4.20 a gallon, Patrick DeHaan, senior analyst for price tracker gasbuddy.com, expects Minnesota to average the priciest gasoline in the continental U.S., overtaking California, which now averages $4.06 a gallon.