Gas prices fall for 13th straight day
Retail fuel prices have fallen nearly 20 cents since July 16, reaching a level not seen since late May.
NEW YORK (CNNMoney.com) -- Regular gas prices at the pump, along with diesel and ethanol, have declined for the 13th straight day, a daily survey of filling station credit card swipes showed Wednesday.
Gasoline: The price of regular unleaded gas at the pump slipped 1.5 cents to $3.926 a gallon on average, a level not seen since late May, according to a nationwide survey from motorist advocacy group AAA.
The average price for regular has fallen 18.8 cents since hitting a record high of $4.114 at the pump on July 16.
Gas prices have been tracking a decline in oil prices. The fall has been sparked by worries that the high cost of fuel is slowing demand.
Gas prices first crossed the $4 mark on June 7 when they hit $4.005 a gallon, AAA data showed.
Ethanol: High gas prices have caused many drivers, particularly those in states with strong agricultural industries, to switch to ethanol as their fuel of choice.
The price of E85, an 85% ethanol blend which burns cleaner than straight gasoline and is made primarily from corn, fell 3.5 cents to $3.166 a gallon on average, AAA reported.
While ethanol is derived from renewable sources, it is less efficient than gasoline. As a result, a car running on E85 would pay the equivalent of $4.167 per gallon to get the same mileage as gas, the AAA survey estimated.
Diesel: The average price of diesel fuel, which is used to power most trucks and commercial vehicles, fell to $4.714 a gallon from $4.724, according to AAA.
Diesel prices have climbed more than 69% in the last 12 months. And because of diesel is used to transport goods, the high prices have affected the prices of other items.
State prices: The AAA survey averages data from credit card swipes at 85,000 fuel stations around the country.
Gas in Alaska, the state with the highest prices, fell to an average of $4.648 a gallon from $4.654 the previous day, according to AAA. Hawaii, the state with the second highest prices, saw average prices rise to $4.50. California prices dipped to $4.288 on average, the AAA survey said.
Drivers in Oklahoma, the state with the cheapest gas, saw prices fall to $3.655 from $3.67 a gallon the day before. In Minnesota, the next cheapest state for gas, drivers paid $3.678 on average, followed by Ohio at $3.693.
Drivers in Hawaii, the state with the most expensive diesel, saw diesel prices rise to $5.398 a gallon. Diesel was cheapest in Oklahoma at $4.488, according to the AAA survey. 
