Gas falls below $3.90 a gallon
Average fuel prices fall for 15th straight day, according to AAA survey.
NEW YORK (CNNMoney.com) -- The price of regular gas fell below $3.90 a gallon as fuel prices fell for the 15th day in a row, a daily survey of gas station credit card swipes showed Friday.
Gasoline: Regular unleaded gas fell 1.1 cents to a nationwide average price of $3.898 a gallon, according to a nationwide survey from motorist advocacy group AAA.
The average price for regular has fallen more than 21 cents since hitting a record high of $4.114 at the pump on July 16, according to AAA data.
Many Americans blame high fuel prices on oil companies and foreign oil producers, according to a CNN/Opinion Research poll released Thursday.
Ethanol: High gas prices have caused many drivers, particularly those in regions with strong agricultural industries such as the Midwest, 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 1.1 cents to $3.144 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 $4.137 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 $4.686 a gallon from $4.698 the previous day, according to AAA.
Diesel prices have climbed more than 58% in the last 12 months, driving up costs for businesses and inflating the prices of the goods and services those businesses provide.
State prices: The AAA survey, which averages data from credit card swipes at 85,000 fuel stations around the country, showed that gas remained above $4 a gallon in 12 states.
Gas in Alaska, the state with the highest prices, rose to an average of $4.646 a gallon from $4.636 the previous day. Hawaii, the state with the second highest prices, saw average prices fall to $4.486. California, the state in third place, saw prices slip to $4.248 on average.
Drivers in Oklahoma, the state with the cheapest gas, saw prices fall to $3.625 from $3.636 a gallon the day before. In Minnesota, the next cheapest state for gas, drivers paid $3.652 on average, followed by Missouri at $3.662.
Drivers in Hawaii, the state with the most expensive diesel, saw diesel prices fall to $5.402 a gallon. Diesel was cheapest in Oklahoma at $4.462, according to the AAA survey. 
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