At www.fueleconomy.gov, for instance, click on "Find and Compare Cars" at the bottom. Use one of the search strategies on the left (by year, make, model, etc.) to pull up the cars you're considering.
Look at their stats side by side, then right-click on your browser page, select "Send link" (may vary by browser) and send your comparison chart to the e-mail address you access from your phone.
As you test drive different cars and determine which ones actually feel right for you, you can look back at the chart to see whether you're falling in love with a gas-guzzler or to finalize the choice between two finalists.