THE Cayenne is an oddity.

Here is a Porsche that isn't a low-slung two-door sports car. But despite its heft, the portly sports-utility vehicle boasts a handling that actually befits the brand, to a point. It seems to reconcile conflicting themes incredibly well.

The SUV has become one of the most successful models for Porsche. That's great news for shareholders, but bad news for dear Gaia.

Back when the Cayenne was launched in 2002, the Turbo version, when used in the city, burnt fossil fuels at the rate of 21.9 litres per 100km - more than three times thirstier than a Honda Jazz.

Porsche hasn't been oblivious to the mounting complaints. It introduced direct-injection to its entire range of engines during the Cayenne's facelift earlier this year to reduce consumption.

But what follows is the most radical step taken by a sports car manufacturer yet: introducing an electric drivetrain to the line-up.

It is a project that started two years ago, in partnership with sister companies Volkswagen and Audi. The VW Touareg and Audi Q7 share the Cayenne's basic architecture, and are equally thirsty.

Porsche unveiled the solution, in the form of a prototype Cayenne Hybrid, at its normally secretive Porsche Development Center last week.

Based on the 3.6-litre V6 model, the Cayenne Hybrid is expected to achieve at least 25 per cent fuel savings when used in the city.

Over test-runs made by invited journalists on the dynamometer, which was programmed to simulate the road conditions around the Stuttgart area, the Cayenne Hybrid averaged between 9.1 and 10.7 litres per 100km.

The target is 8.9 litres by 2010, when the Cayenne Hybrid will be launched. The Lexus RX400h is capable of achieving that today, but it is smaller and lighter.

Vital to Porsche's concept is how the Cayenne Hybrid has preserved the sporting driving flavour expected of the marque.

The engineers claimed to have managed to seamlessly blend changes in the driving forces, which can vary from purely petrol engine, electric motor or a mix of both. But it's still discernible.

When accelerating hard, the introduction of electric power to the drivetrain is discernible, but the system has been cleverly engineered to effect a downshift on the six-speed Tiptronic transmission as well. This serves to partially mask the transition as well as to maximise the explosive effect of the additional jab of power.

A ride round the Weissach test track reveals a Cayenne that seems almost as urgent as a 4.8-litre V8 model, with the powerful electric motor convincingly fattening up the torque curve of the 3.6-litre engine.

The Cayenne Hybrid isn't the only fuel-efficient and tax-friendly Porsche that fans can look forward to. Engineers expect new battery technologies will allow hybrid drivetrains to make their way into other sports cars.

At Porsche, the upcoming four-door luxury sedan, the Panamera Gran Turismo, will have a hybrid variant.