BOSTON — The cost of filling up the gas tank in the Bay State continues to go down in September.

According to GasBuddy's daily survey of 2,830 stations, Massachusetts gas prices have fallen 1.5 cents per gallon in the past week, averaging $2.55 per gallon on Monday. Gas prices in the state are 9.9 cents per gallon lower than a month ago, yet stand 31.7 cents per gallon lower than a year ago at this time.

According to GasBuddy price reports, the cheapest station in Massachusetts is priced at $2.19 per gallon while the most expensive is $3.39, a difference of $1.20 per gallon. The cheapest price in the entire country today stands at $1.80 per gallon, while the most expensive is $4.99 per gallon.

The national average price of gasoline has fallen 0.4 cents per gallon in the last week, averaging $2.55 per gallon on Monday. The national average is down 6.5 cents per gallon from a month ago, yet stands 28.9 cents per gallon lower than last year.