Thanks +John Scott
, I didn't know that, but I should just applied the usual principle: Europe always gets the best diesels! I did research and see a plug-in Volvo diesel hybrid, as well as a diesel hybrid Range Rover, both both of these are relative gas-guzzlers.
In any case, that confirms what I was speculating on in my first post-- 2x the mpg if you use a diesel as the internal combustion engine. Combine that with biodiesel and you are beginning to approach sustainable transportation for the Single Occupancy Vehicle.