Designed in the 1970's in California (USA) by Subaru of America (possibly by Alex Tremulis) with the Vehicle Research Institure (VRI). The Subaru X was an experimental prototype capable of 100 mpg.  The vehicle, a single seater, was tested in Japan by a female Japanese racing driver where it achieved 100 mpg. It was also tested at the Ontario Motor Speedway in 1980 where it is reported to have achieved 100.2mpg using a 544cc 2-cylinder, 4-stroke engine.

The vehicle is still owned by Subaru.

The Subaru X. (My thanks to Arak Leatham for sending in this picture - at the time he was an intern at the "VRI" and acquired this photo.)