Fuel economy probably is the #1 reason why people choose to buy diesel passenger vehicles. Gas/electric hybrids provide a fuel efficient alternative.
Case in point: the Porsche Panamera S E-Hybrid. The E-Hybrid pairs a twin turbo V6 gas engine with a plug-rechargeable electric motor that is powered by a lithium-ion battery. The result is a luxury 4 passenger sedan that can reach 60 mph in 5.5 seconds, has a top speed of 168 mph, and can average 53 miles per gallon of gas consumed. The vehicle can drive about 22 miles on battery power alone. The battery can be recharged in about 2.5 hours from a 240V charger.
That mpg figure is the average of 42 test runs by automotive journalists who recently logged about 750 miles around a test loop in Germany. The route included city streets, country roads and no-speed-limit autobahn. Each vehicle carried 3 or 4 passengers. In other words, this is a real world test, not a laboratory exercise.
Porsche doesn't make a diesel powered Panamera. A similar vehicle is the Mercedes S350 Bluetec diesel, which is EPA-rated at 31 mpg in highway use. The new Audi A8 diesel is rated at 36 mpg highway. It will be interesting to see what EPA rating is assigned to the Panamera S E-Hybrid when it arrives in USA in late 2013.
The only sticking point with these sedans is price. The Panamera S E-Hybrid list price starts at $99K.