Denver gas prices still below U.S. average. With an average price of $2.62 per gallon, the average price for a gallon of gas in Denver is still well below what the rest of the country is paying.cross the country, the average price of a gallon of gas is $2.751 per gallon, according to Coloradgasprices.com. But Denver gas prices have risen in the past few days (on Sunday, the average price was $2.58 per gallon). A year ago, Denver residents were paying an average of $3.424 for a gallon of gas, according to AAA.