The Peel P-50 -- A Really Small Car

The Peel P-50 is officially certified as the world's smallest car by Guiness.

Passenger capacity 1 (plus one shopping bag).
Doors 1.
Wheels 3.
Displacement 50 cc.
Empty Weight 130 lbs.
Fuel Efficiency 100 mpg.

Described in this CNET article and in the very amusing BBC video...

Judging by the video it might benefit from outriggers and some pollution controls.