A weakening market for crude oil and the resolution of U.S. refinery issues has pushed retail gasoline prices down for 20 days straight, motor club AAA found.

AAA reports a national average retail price for a gallon of regular unleaded at $2.64 per gallon, about one cent less than Monday and 5.4 cents, or 4.3 percent, less than one month ago.

AAA said most markets are seeing drops in gasoline prices that are mirroring the decline in crude oil prices, which are down more than 20 percent since July 1. Retail gasoline prices elevated somewhat during the July 4 holiday weekend, but AAA expects the opposite trend leading up to the Labor Day holiday in early September.

"Drivers are paying the lowest averages for this date since 2009, and today's national average represents a savings of 85 cents per gallon compared to this same date last year," the motor club said in a weekly price report. "The national average is now 15 cents per gallon lower than the 2015 peak price of $2.80 on June 15."

South Carolina posted the lowest state average for Tuesday with $2.26 for a gallon of regular unleaded gasoline.

AAA said it expects crude oil prices to stay low because of concerns about the slowdown in the Chinese economy and the expectations that more Iranian oil could enter the market as a result of last month's multilateral nuclear agreement.

"Weaker growth means lower than projected oil demand, which could further increase the glut in global petroleum supplies," the motor club said.