I know Matt Haughey bought a database of cars for developing <a href="http://www.fuelly.com/>Fuelly</a> http://www.fuelly.com/>Fuelly</a>, whose entire purpose

I know Matt Haughey bought a database of cars for developing <a href="http://www.fuelly.com/>Fuelly</a> http://www.fuelly.com/>Fuelly</a>, whose entire purpose is evaluating fuel efficiency of different cars. I'm not sure where he got the database, but I think he wrote about it somewhere. And you could always ask him. I don't know that they have a public API, but Matt's a great guy, and might have some form of an API available if you connect with him. He's @mathowie on Twitter / everywhere.