I know, I know. Gas prices suck.

But before you rush out to invest in one of those nifty flexible-fuel vehicles the commercials have been telling you all about, think about this: a flexible-fuel vehicle won't relieve the pressure on your pocketbook.

In fact, it could end up costing you more in the long run.

Flexible-fuel vehicles, such as the Chevy Tahoe, GMC Sierra, Dodge Ram and Jeep Commander, can run on either regular gasoline or E85, a fuel blend made by combining gasoline and ethanol.

Most vehicles can run on a mixture that is 90 percent gasoline and 10 percent ethanol, but only specially designed vehicles can accommodate E85, the most widely available alternative fuel in the U.S.

E85 is 15 percent traditional gasoline and 85 percent ethanol, a fuel that's both renewable and can be produced domestically. E85 is supposed to be better for the environment than traditional gasoline, and at first glance it looks like a bargain.

E85, according to AAA, was selling for about $2.51 a gallon at the time I wrote this column, 50 cents below the national average price of $3.01 for a gallon of regular unleaded.

But if it looks too good to be true, it's because it is.

Each gallon of E85 you buy might cost you less at the pump, but it won't take you as far as a gallon of the plain old regular unleaded stuff.

Ethanol has a lower energy density than gasoline, which means fewer miles to the gallon for motorists.

The Environmental Protection Agency estimates ethanol blends cut fuel efficiency by as much as 25 percent in many vehicles, a fact that can erase much of the savings brought by buying a cheaper gasoline blend.

There's no point in paying less per gallon if you're going to have to buy more gallons to get where you're going.

The way AAA calculates it, it plays out like this: A gallon of E85 that you pay $2.51 for at the pump actually costs you the equivalent of $3.31 a gallon.

All of a sudden, E85 doesn't sound so good.

At the equivalent of $3.31 a gallon, E85 ends up costing more than even the average prices of mid- and premium-grade gasoline. Not to mention the fact that gas stations carrying E85 aren't exactly on every street corner.

Only six E85 fueling stations are located within a 100-mile radius of San Antonio, according to the National Ethanol Vehicle Coalition.

The idea of using a renewable fuel that costs less per gallon is a great and noble one and one that should continue to be explored.

Unfortunately, it's not the best bet for consumers looking to save a few bucks — at least not yet.