Volkswagen made big claims about the efficiency of their purpose-built XL1 diesel-hybrid. They claimed the car was good for 314 mpg, which equates to 0.9 l/100km in the Metric system. However, at a recent test drive event organized by VW, a handful of journalists were given the chance to drive the mid-engined XL1.
It's not all bad news. Autocar were also at the event and report that on an early test drive, which including crossing a mountain range, the most economical drivers achieved a real 188 mpg and conclude there’s surely potential for 200 mpg on a long motorway run.
The upshot is that the plug-in hybrid XL1 is probably still the most economical and most aerodynamically efficient production car of all time.