Gas was selling at $3.667 a gallon on average, down from $3.672 a day earlier, according to motorist group AAA and the Oil Price Information Service.
Prices have fallen more than 10% since hitting a record high of $4.114 on July 17, AAA reported.
The decline in prices at the pump followed a more than 20% decline in the price of crude oil -- the main ingredient in gasoline.
Oil prices have declined as commodities investors worry that the high price of fuel is causing drivers and businesses to cut back on the use of gasoline and diesel fuel.
Those concerns have driven gas prices below $4 a gallon in all but two states: Alaska, where gas was selling at $4.546 a gallon, and Hawaii, where gas was $4.393 on average.
The lowest average gas prices were found in Missouri at $3.424.
Gas prices can vary from state to state due to differences in state and local gasoline taxes, and proximity to oil and gas facilities around the Gulf of Mexico.
Despite the drop in price, gasoline remains more than 33% more expensive than it was last year, according to AAA.
Diesel: The average price of diesel fuel, which is used by most trucks and commercial vehicles, held steady at $4.283 a gallon compared to the day before, the survey said.
Because of its use in shipping and transportation, high diesel prices can boost the prices of goods and services as businesses pass along extra costs to their customers.
The average price of diesel was most expensive in Hawaii and Alaska at $5.288 and $5.112 a gallon, respectively. Diesel was cheapest, on average, in Missouri at $4.036.
Diesel prices have also fallen with crude oil prices since July, shedding more than 56 cents. But they remain more than $1.36, or 46% higher than they were a year ago, according to the AAA survey.
Ethanol: The price of E85, which can substitute for gas in specially configured "flex-fuel" vehicles, fell to $3.03 a gallon on average, AAA reported.
The high price of petroleum-based fuels has raised the profile of alternatives such as E85, an 85% ethanol blend.
Ethanol is made primarily from corn, not volatile crude oil, and is cheaper per-gallon than gasoline. However it's difficult to find outside the corn-producing Midewst, and it's not sold in some states.
E85 also has a lower energy content than gas. Drivers would have to pay the equivalent of $3.987 a gallon for E85 to get the same mileage as gasoline, AAA estimated.
