Gas prices are down slightly this week across Arizona. Triple-A Arizona says the average price of gas in the state is $2.82 a gallon, which is down a cent from last week. In Flagstaff gas prices are down a cent-and-a-half from last week to $2.75 a gallon. However, some stations are selling gas for $2.65 a gallon and lower. In Prescott, gas is down over two cents a gallon on average to $2.90 a gallon. However, some stations are selling gas for $2.84 and lower. Officials say an increase in gasoline supply has helped keep prices in check and heading lower.