Maine gas prices have plummeted nearly six cents per gallon in the past week, to an average of $3.64. Price-monitoring website MaineGasPrices.com reports Monday the average retail gasoline price in Maine is now just six cents above the national average of $3.58. In-state prices are now more than 33 cents lower per gallon than at the same time last year and nearly 15 cents per gallon lower than a month ago. Nationally, prices are nine cents lower than a month ago. The Maine price is based on a survey of more than 1,200 gas stations.