The cost of a gallon of gas in Maine has shot up nearly eight cents in the past week. Price-monitoring website MaineGasPrices.com reports Monday that the average retail cost of a gallon of gas soared to $3.78 in the past week. While gas prices are rising nationally, the average cost rose faster in Maine and is now 11 cents higher than the national average. Prices are now more than seven cents per gallon higher than the same day one year ago and 28 cents per gallon higher than a month ago. A company analyst blames higher prices on problems at oil refineries. The good news is that the summer driving season is almost over and cheaper winter blends will soon hit the market.