The national average price for a gallon of gasoline is up 7 percent in August, according to AAA. The average price rose to $3.75, up from $3.49 per gallon in July. Des Moines’ average price of $3.67 per gallon is below the national average, but up 4.6 percent from $3.50 per gallon in July. At an average of $3.67 per gallon, Iowa had the 19th cheapest gas in the nation. Hawaii had the highest priced gas at $4.28 per gallon, while South Carolina had the cheapest gasoline at $3.48. For the month of August, Iowa residents spent 7 percent of their income on gas. Click here to see a full state breakdown.