The cost of a gallon of gas in Maine continues to skyrocket, and is rising faster than the national average. Price-monitoring website MaineGasPrices.com reports Monday that the average retail cost of a gallon of gas in Maine jumped more than seven cents in the past week to $3.79. That compares to a national average that rose about 3 cents. Maine residents are now paying 11 cents more at the pump than the national average. In-state prices are now 17 cents higher than on the same day last year and almost 23 cents higher than a month ago. The Maine price is based on a survey of more than 1,200 gas stations.