The Environmental Protection Agency (EPA) has taken the final step in approving 15-percent ethanol blends for sale to consumers at gas stations nationwide, effective immediately. However, state and local regulations, as well as liability uncertainty, remain barriers to its adoption.

It has taken years for this milestone to be reached. First, the agency approved the fuel for use in 2007 and newer cars and trucks in 2010. Then in January 2011, it expanded the approval to all vehicles made since 2001.

Last July the agency devised a label that would be required on pumps selling E15, so consumers who drive older cars would be able to tell the difference. In April, EPA approved the production of E15.

Various organizations have opposed the sale of E15, citing engine durability concerns, consumer confusion, and concerns about small engines in lawn mowers and other power equipment.

While E15 could be an effective way to reduce petroleum consumption on a national basis, blending additional quantities beyond E10 poses compatibility hurdles with both infrastructure and vehicles. As a liquid fuel that has been produced for centuries, ethanol should require the fewest changes from traditional petroleum of any available alternative.

In our own testing, Consumer Reports found that a flex-fuel vehicle specifically designed to run on E85, a much higher blend of ethanol, got almost 30-percent worse fuel economy running on the fuel than it did on regular gasoline. Perhaps lower mid-grade blends could provide some advantages without such a large drop in fuel economy, but the energy density of ethanol is significantly lower than gasoline.

Consumers Union, the consumer advocacy arm of Consumer Reports, has expressed concern about warranty coverage for consumers who mistakenly fuel their cars or small engines with E15. But the organization remains hopeful that a solution can be found that will protect consumers and add another arrow to the country's arsenal of alternatives to its dependence on petroleum from other parts of the world.

See our guide to alternative fuels.