BMW has unveiled the latest offering in the car- of-the-future stakes.

Destined to make its first public appearance at the Los Angeles Motor Show at the end of this month, the new car will be familiar to fans of the company's 7 Series model.

Called the Hydrogen 7, the clue as to the car's fuel source is in its name. Based on the existing 7 Series, it comes with an internal combustion engine capable of running on liquid hydrogen or petrol. In hydrogen mode, the car emits nothing more than water vapour.

Powered by a 260hp 12-cylinder engine from the 760i variant, the Hydrogen 7 accelerates from zero to 62mph in 9.5 seconds before going on to an electronically limited 143mph top speed.

The Hydrogen 7 will be built in limited numbers and offered to selected users in 2007 as part of a global trial to better understand how such a car will perform in everyday situations.

Engine power and torque in the Hydrogen 7 remain exactly the same, regardless of which fuel is in current use. The driver can switch between the two without any noticeable effect on performance. The car always gives priority to the use of hydrogen but, should this run out, it automatically switches to petrol power.

With its dual power engine, the car has a cruising range in excess of 125 miles in hydrogen mode, with a further 300 miles under petrol power.

To make this possible, the BMW Hydrogen 7 comes with a conventional 74-litre petrol tank and an additional hydrogen fuel tank holding up to 8kgs of liquid hydrogen located between the boot and rear seats.

Given the fact that hydrogen filling stations are still a rare sight - although car companies and other agencies are currently seeking to improve the situation - such flexibility should mean the driver of a Hydrogen 7 is able to use the vehicle at all times, even when the nearest hydrogen station is out of range.

Unlike many other hydrogen cars being touted by rival companies, BMW is keen to stress that the Hydrogen 7 is as close to a production vehicle as is possible.

Developed in the same way as other BMW cars, this special 7 Series is built on a conventional production line - albeit in run that will top out at 100 units.

Details of the trial programme and the destinations of the 100 cars - it's expected many will end up in the hands of politicians, business leaders and environmentally aware celebrities and sports personalities - will be announced at a later date.