As a Toyota Corolla owner I sometimes find myself thinking whether I should buy a Toyota Prius, the gas/hybrid model that has won many accolades for its efficiency and "economic value."

I understand and sympathize with all the political reasons out there to drive a hybrid car. I also would like to lessen our dependence on foreign oil and narrow the foreign trade deficit.

But how much individual economic sense does a Prius really make over a Corolla?

More specifically, how many years do I need to drive a Prius to earn back the extra purchasing price I'd be forking up front?

The results convinced me to stick with my Corolla, at least for a while.

Would you still buy a Prius if you knew that you have to drive it for 7 years to get back what you have paid extra at the dealer? I wouldn't.

Here is my analysis:

To make the comparison as conservative as possible, I'll compare Prius ($21,725) with the most loaded-up and expensive Corolla model available - the XRS ($17,880), in an effort to minimize the difference in upfront costs.

Other assumptions I'm making: you drive 15,000 or 25,000 miles a year and pay $3 for a gallon of gas.

I'm also taking 38 mpg as Corolla's average highway mileage despite the fact that the official Toyota figure is 41 mpg. I know for a fact that Corolla does get 38 mpg. But I wasn't so sure about the 41 mpg figure. So I went with a more conservative figure that I was comfortable with.

The below table shows that if you drive your car for 25,000 miles a year, you would have to drive your Prius for seven (7) years before you recoup the extra dollars you pay for buying it instead of a loaded Corolla XRS.

(See the table at http://writer111.googlepages.com/PriusComparisonTable.jpg)

If you drive less, or if you buy a much-cheaper Corolla CE, you may have to drive up to 25 years to get your money's worth!

I usually keep a car for about 7 or 8 years.

I'm willing to drive a Prius the first 3 years "in the red," for the sake of "helping the environment" and easing off our foreign trade deficit.

But after three or four years I expect to see some real savings to justify Prius as a "more economical" alternative to Corolla.

And for that to happen, the initial price difference between the two models (for a 15,000 miles a year driver) has to come all the way down to $700, not the current $3,800-plus.

Until then, Prius will be a "political" and not an "economical" choice for me.