A new Web tool helps users compare car rental models based not just on the rental price but on the estimated amount they will have to pay for gas, according to SmarterTravel.com.

Meta travel search engine Kayak rolled out the Web tool, which allows to click on the "fuel cost calculator" and enter in how many miles they plan to drive on average each day and whether that driving will be primarily city, highway, or both. The tool then recalculates the daily price of each car rental to include the estimated daily cost of gas. This estimate also takes into account the average miles per gallon each car rental model gets.

The Fuel Cost Calculator is available on the results page of its rental car search at kayak.com/cars.

A separate search function allows users to eliminate car models that get below a certain mile-per-gallon rate.

SmarterTravel.com writes that the site seems to use the same average price per gallon of gas for all searches, no matter the location. The site says that can be a problem because prices can be a lot higher in places such as major West Coast cities, and lower in places like Texas.