Next week’s Frankfurt auto show will see “green luxury” vehicles out in full force.

Joining Lexus and Infiniti, German premium brands Audi, BMW, Mercedes-Benz and Porsche will unveil up-and-coming high-end hybrid models.

Mercedes’ recent announcement of its S500 Plug-in Hybrid is just the latest example of how quickly the bar is being raised in short intervals. The auto maker will display the show car in Frankfurt ahead of a production-ready version expected to go on sale late next year.

The S500 combines roominess and comfort with fuel economy of 77.6 mpg (3.0 L/100 km) and just 69 g/km of carbon-dioxide emissions. The sole compromise is less room in the luggage compartment.

Mercedes adds the S500 PHEV to its S-Class hybrid lineup that includes the S400 Hybrid and S300 BlueTEC Hybrid. All second-generation hybrid-drive systems share seamless integration into the powertrain, an improved recuperative braking system and the anticipatory intelligent-hybrid energy-management system.

However, it is the top-shelf S500 that "sets another milestone on the road to emission-free mobility on the basis of our modular hybrid matrix," says Thomas Weber, head of product engineering- Mercedes-Benz Cars. "In this way the S-Class turns into a genuine 3L car with generous space and superlative drive-system comfort."

While the batteries of the S300 and S400 as autonomous hybrids are charged during braking or coasting or by the combustion engine, Mercedes says the new high-voltage lithium-ion battery of the S500 has 10 times the energy content and offers the option of being recharged from an external source with a socket located on the rear bumper.

The 80-kW (107-hp) electric synchronous motor, mated to a 3.0L turbocharged V-6 gasoline engine making 328 hp, gives the S-Class a range of about 18 miles (30 km) on electric power alone. It reaches 60 mph (97 km) in 5.5 seconds and its top speed is 155 mph (250 km/h).