NEW YORK ( MainStreet) — More Americans are on the road this holiday season as year-end travel reaches record levels, according to the AAA. Most of us – fully 91% -- are traveling by car, and that means quite a few visits to the gas pump. Ethanol is a growing ingredient in the fuel mix we pump into our tanks – but the AAA is warning drivers about the "potentially negative" effects ethanol-blended fuels can have on our vehicles.

Most of the gasoline sold in the U.S. is E10, a low-level blend of 10% ethanol and 90% gasoline. Some "flex fuel" vehicles can take E85 gas, which is a high-level blend containing 51% to 83% ethanol, according to the U.S. Department of Energy. But showing up more often at the pump is an E15 blend of 15% ethanol, and the AAA is concerned with the way the industry has introduced and marketed E15 to consumers.

In 2011, the EPA approved E15 for use in 2001 and newer vehicles, but the AAA says it's not always a good way to fill up.

"Most drivers are unaware of the potentially negative effects of E15 and have not been properly educated about this new fuel," says the AAA. "More than 90% of the vehicles on the road today are not approved by manufacturers to use E15, including nearly all 2001-2013 models."

The not-for-profit travel organization says E15 should only be used in flex-fuel engines, which include 2001 and newer Porsches, and selected 2012 and newer vehicles.

"Sustained use of E15 gasoline in vehicles not designed for its use could result in significant problems such as accelerated engine wear and failure, fuel-system damage and false check engine lights," AAA says. "Automakers are on record as saying their warranties will not cover claims caused by E15."

While newer model vehicles are increasingly compatible with E15 blended gas, the AAA says previous makes and models were never designed to use the fuel. The association claims it will take at least another decade before the bulk of America's vehicles will be tuned for E15 gas.

Ethanol producers are looking to expand sales of E15 gasoline in an effort to meet the federal Renewable Fuels Standard (RFS). The RFS requires renewable fuels such as ethanol to be blended into gasoline in increasing amounts each year.

Blenders unable to meet RFS requirements would be subject to significant fines, which could restrict gasoline supplies and result in significant increases to gas prices.

The AAA is seeking a reduction in requirements to the Renewable Fuels Standard for next year saying, "While ethanol has the potential to support the economy and reduce the reliance on fossil fuels, it is irresponsible to mandate more ethanol than cars can safely use."