[jyl]

sammy's numbers are valid if you ignore gasoline inflation, which is a pretty major assumption.

Here's the picture including gasoline inflation. Take a Civic w/ 32 MPG (average city and hwy per sammy's numbers), and a Civic Hybrid w/ 44 mpg (avg), assume 20K miles/year, assume year 1 gas is $3.50/gal. Plug in an annual gasoline inflation assumption. If you use 0%, as sammy does, then by year 10 the cumulative gas cost savings is $5,966. At 5%, $7,504. At 10%, 9,508.

Suppose you drive more, 25K miles/yr, then gas inflation 0% gives $7,457 cumulative gas cost savings by year 10, 5% $9,380, 10% $11,885.

Just eyeballing the chart I posted, gas inflation has been about 10% over the past decade.

Obviously there is the question of how long you'll keep the car. If you sell it after a short time, hybrids have higher resale value. If you keep it for a long time, somewhere after 150K miles (typically, if it is <100K mi it is warranty covered, maybe <150K in CA) you need to budget for a battery (don't know about the Civic, for Prius these are appx $3K), and on the conventional car there is repair cost to budget for also.