APART from one or two refinements, the engine that powers your car is not vastly different from the design patented by Gottlieb Daimler and Wilhelm Maybach back in 1885.

Perhaps that is because, until recently, there seemed little reason to change. Petrol and diesel are excellent sources of power and, as long as oil remained cheap and plentiful, it was hardly sound business sense to spend billions researching an alternative.

But things are changing - and fast. The earth's oil reserves are depleting faster than anyone expected and exhaust emissions are causing irreversible changes to the world's climate.

Toyota - the world's second largest car company - is at the forefront of moves to do something about that. The Japanese company introduced a hybrid propulsion system six years ago.

Once it had worked the bugs out of the system, it moved to phase two - selling hundreds of thousands of petrol/electric hybrids - with consequences that were most unexpected.

The car that pioneered Toyota's hybrid technology - the Prius - has become one of the coolest vehicles on the planet.

Owners have taken it to their hearts. Websites are dedicated to evangelising just how good a Prius really is ("This is the greatest car ever invented" one comment on Priuschat.com reads) and famous people are flocking to get behind the wheel. In no time at all, Toyota's green machine has become the four-wheeled equivalent of Apple's iconic iPod. Everyone wants one - and not just Hollywood A-listers, such as Tom Cruise, but ordinary folk who do not care about the technology ("It is a Toyota, so it will go on forever, right?"). They just want a car that achieves 50mpg and makes them feel good about saving the earth.

No wonder Toyota is doubling production and building a factory in China dedicated to making more hybrids.

Toyota is not the only company in this market - Honda has a Civic, an Accord and the Insight hybrids - but it is by far the most successful.

As well as the Prius, it also markets the Lexus RX400h, the first luxury 4x4 that proved a hybrid engine can be powerful as well as frugal. Ernest Bastien, vice-president of Toyota vehicle operations, revealed why the company was spending billions on this new technology.

"We are at the edge of making the internal combustion engine similar to regular film for 35mm cameras," he said.

Some European manufacturers have rejected hybrids as an automotive dead end. Not so much a digital camera as a Polaroid instamatic. They believe the future lies with hydrogen fuel cells.

But hydrogen is expensive to make and selling it would require a whole new fuel station infrastructure. The hybrid can work with what is already available, which is why Toshiba recently committed $95m to build a manufacturing plant dedicated to hybrid control system microchips, and it is also why Sanyo is investing heavily in the battery technology used by the Prius.

And that technology is getting better all the time. The second generation Prius was 25 per cent more efficient than its predecessor. New battery technology is on the way that will make hybrids more effective still.

Some of the world's largest carmakers seem to agree. Ford and Nissan have licensed Toyota's technology to use in a range of their cars. General Motors is also ploughing billions into hybrid research to try to make up lost ground on Toyota.

Ten years from now, car buyers who fancy a hybrid will be spoilt for choice.

Perhaps in 20 years' time, the internal combustion engine as it is now will be gone forever. After all, only five years ago, no one thought 35mm film cameras would be approaching obsolescence by 2006.