I never quite understood hybrid cars other than buying them as an indirect donation to pursue hybrid technology. Hybrids are worse for the environment than regular plain-ole' ICE cars and don't really give you much of an efficiency boost.

Diesel engines are right up there with hybrids in the fuel efficiency game. Take for instance to VW Polo BlueMotion which is rated 70mpg+ Highway. The Passat BlueMotion is worse but still an impressive 57mpg+ Highway.

Also consider that some biodiesel fuels are near 100% carbon neutral (such as hemp-based biodiesels), in that they sequester as much carbon dioxide from the air as they will eventually burn into once combusted.