The fuel efficiency of plug-in hybrids, at least in terms of MPG, largely depends on the distance to be drive, the miles of electric-only range of the vehicle and the  ability to recharge along a route.

All Alone on the Open Road...No Not Really...Some Cropping May Have Been Used Here

All Alone on the Open Road...No Not Really...Some Cropping May Have Been Used Here

Therefore, it's difficult to say that plug-in hybrid X gets Y-ish MPG and that plug-in hybrid A gets B-ish MPG.

The variables are ever-changing, especially out there in the real world.

We premise it this way because Porsche has published the first real-world MPG figures for its Panamera S E-Hybrid.  Porsche plug-in hybrid sedan was recently driven  by journalists and the MPG results are in.

All the nitty-gritty details of the first test drives are described by Porsche below:

"Stuttgart. On the occasion of an international press event – in which over 42 test drives were conducted with journalists in the Panamera S E-Hybrid covering a total distance of over 1,200 kilometres – the model consumed just 4.4 l/100 km averaged over all drives. The top value recorded on the circuit course for the world's first plug-in hybrid in the luxury class was a low 2.8 l/100 km. These results illustrate that in real everyday operation, it is entirely possible to attain fuel consumption values of the same magnitude as the value determined in NEDC testing, which is 3.1 l/100 km. And it even accomplished this in four unmodified Panamera S E-Hybrid production cars, each carrying three to four persons, with the climate control system activated and accelerating up to 230 km/h on the motorway section of the route. The test circuit, which had a total length of 28.7 km, followed a course through and around the city of Hockenheim and comprised 6.5 km city driving, 9.2 km of country roads and 13 km of German Autobahn – some without speed limits. A prerequisite for attaining such values is systematically exploiting opportunities for charging the 9.4 kWh lithium-ion battery on the electrical grid."

In terms of MPG, the results of the 42 test drives averages out to 53.45 MPG.

Unfortunately, Porsche doesn't say how often the plug-in Panamera was charged, or if it even ever was during the 28.7 km loop.

We've purposefully left these figures in metric, because Porsche offers up this additional info, which shed some light on the overall fuel efficiency marks achieved in these tests:

"The car's range of 36 kilometres in all-electric driving was also confirmed in practice with a fuel consumption value of 0.0 l/100 km and zero local emissions, which was not only attainable in NEDC testing on a dynamometer, but also on the street. And it even attains this value at an average speed of 54 km/h, while the average speed in NEDC testing is just 33 km/h."

The Panamera S E-Hybrid will be at dealers in mid-Summer 2013.  Its base MSRP of $99,000 represents only a $6,000 premium over the non plug-in version of the Panamera S.