Narration: This, I'm embarrassed to say, is my car.

Dr Jonica Newby: This seat is operated by a spanner ... windscreen wiper fell off last week the back door doesn't open.

Narration: Obviously I need a new car - but which?

It's a decision most of us face in the next 5 years, only this time it won't be a simple choice of brand.

With oil heading for decline, and greenhouse gases soaring, the burning question is - what's going to replace petrol?

Dr Jonica Newby: So I've come to California, hired a 20th century gas guzzling fossil fuel dinosaur... and we're heading out on the ultimate road trip in search of the world's next car fuel - and my next car

Narration: Why California? Well, to answer that, let's hear from the Governator himself.

Governor Schwarzenegger: We are committed to rolling back our greenhouse gas emissions to the 1990 level by the year 2020.

Narration: California is taking a rebel lead on global warming. And with transport producing 40% of all greenhouse gases, legislators here are forcing car companies to make low emissions cars.

Governor Schwarzenegger: "Our cars have been running on dirty fuels for too long. Our country has been dependent on oil for too long."

Narration: And now, I'm heading for Los Angeles to see one of the hottest petrol replacing contendors.

This is what I've crossed the world for.

This is the Tesla!

Dr Jonica Newby: I'm not even into cars - but this - this is seriously exciting. This car can go from zero to 100 kilometres per hour in just 4 seconds - that's faster than a Lamborghini. And would you believe, this car is 100% powered by electricity.

Narration: Hang on - didn't the electric car die? In the recent film "Who killed the electric car", they even held a funeral.

Dr Jonica Newby: Well, to hear the extraordinary tale of death and resurrection, let's meet the man who made the film, electric car activist, Chris Paine.

So this is an electric car. Isn't the electric car dead?

Chris Paine: Well yes. This generation of electric cars died and actually the previous generation of died too.

In fact electric cars were the first cars on the road but by 1920 the gas car had pretty much taken over. It wasn't until nineteen ninety that a new generation of electric cars came out - really amazing cars - but unfortunately electric cars take on a lot of business interests that are threatened by them.

Narration: In 2004, General Motors crushed its own electric car fleet. It seemed the electric car dream was finally over.

Chris Paine: It was very sad because you saw incredible technology being snuffed out for very stupid reasons.

Narration: But then, out of nowhere, emerged the Tesla. And it's not just the power that makes this car revolutionary.

Until now, electric cars had a range of just 60 miles. This car can go 250 miles on a single charge.

So what changed?

The man with the answers is the driving force of Tesla motors, Martin Eberhard.

Dr Jonica Newby: Is it proving popular? Martin

Martin Eberhard: Very much so.

Narration: Eberhard realised the evolution of computers had brought a revolution in batteries rechargeable lithium batteries.

Martin Eberhard: Right. So inside your, your, your computer you would find 4 or 6 or maybe 8 of these - in the car there's a few more, yes

Dr Jonica Newby: How many, how many of these?

Martin Eberhard: Nearly 7000

Dr Jonica Newby: 7000 of these to fire that one car !

Narration: Electricity is so much more efficient at running an engine than petrol, even if it's sourced from coal, you halve greenhouse emissions.

Dr Jonica Newby: That's pretty exciting, I think I'm sold.

Narration: But even if I could afford the $100,000 dollar price tag for the Tesla, there's a major drawback.

Dr Jonica Newby: Now, if I run out of petrol, which in my shonky car happens embarrassingly often, I can call roadside service or take a can to a petrol station. But if I run out of charge well to use a technical term I'm stuffed.

Narration: That's why the Governator likes a fuel.

Governor Schwarzenegger: That's why I launched California's Hydrogen highway. We already have several hydrogen fueling stations in our state but we are investing millions more

Narration: Next stop, UC Davis, to meet alternative fuel expert, Professor Dan Sperling.

Dr Jonica Newby: So this is part of the hydrogen highway? Dan Sperling: Well not only that, it was the very first station on the Californian hydrogen highway.

Narration: Hydrogen has long been the front runner to replace petrol.

This car is a prototype, but the first commercial Hydrogen car has just been released in Germany - though it'll set you back a few Euros.

At the heart of the Hydrogen car is the fuel cell.

Professor Dan Sperling: Well a fuel cell is in many ways a very simple device, it takes hydrogen and converts it to electricity, and electricity drives the, the vehicle because it's an electric vehicle, electric motors - and water is the only by-product

Narration: But hydrogen isn't the only new fuel on the block.

Professor Dan Sperling: This is the UC Davis Bio-gas plant. It takes waste like food and paper and converts it into energy.

Narration: There are biofuels such as biodiesel from waste, or ethanol from sugar or corn.

But the greenhouse benefits of many biofuels are disputed - and we simply can't grow enough. And hydrogen too has flaws.

Dr. Joe Romm: You need 5 miracles to happen in order to make hydrogen work; you have to solve the fuel cell problem, and they're very expensive, you need a major breakthrough; you have to solve the storage problem

Narration: Dr Joe Romm is the US former acting assistant secretary of energy.

Dr. Joe Romm: Hydrogen's quite expensive; someone has to build all the hydrogen fuelling stations; and then, for hydrogen cars to succeed, all other alternative fuel vehicles pretty much have to fail.

Narration: Even hydrogen supporters admit it's decades away from being widely viable.

So isn't there a technology that's ready to replace my gas guzzler now?

Well, there is one.

It's a hybrid car, but not as we know it.

It's a plug in hybrid and the pioneer who's been developing them for the last 30 years is Engineering Professor, Andy Frank.

The beauty of the plug in hybrid is that the gasoline engine is just a backup - the car travels the first 100 km purely on electricity.

Professor Andrew Frank: What we're doing is we're driving only on electricity at this moment

Dr Jonica Newby: Really, so ah, cost per mile is like, you know, like one 8th the cost of using gasoline in Australia [chuckles]

Narration: If that sounds good, imagine the extra savings - and greenhouse benefits you'd get - from going solar.

Dr Jonica Newby: So you could actually generate all your power, house and car, from your own roof?

Professor Andrew Frank: That's correct.

Dr Jonica Newby: I find that utterly inspiring, I really do.

Professor Andrew Frank: Well, we have to get the car companies to build these things.

Narration: For 30 years, that's been a losing battle.

But then we heard something so extraordinary, we had to take a detour to the City of Cars itself Detroit.

Dr Jonica Newby: Well, my road movie seems to have turned into a bit of a thriller. We've been picked up and we're being taken to a secret location, it's a place film crews have hardly ever been allowed to get into // this could be the world's first glimpse of the car we'll all be driving in just a few years time.

Narration: We're heading into the high security design studios of the world's largest car company - General Motors.

Head of development, Jon Lauckner, has just committed to producing the world's first commercial plug in hybrid within a couple years.

Dr Jonica Newby: So this is it?

John Lauckner: This is it

Dr Jonica Newby: So this is our Chevrolet concept car to demonstrate our new eflex propulsion system, it's the first application of eflex.

Dr Jonica Newby: Eflex meaning?

John Lauckner: E' standing for electric and 'Flex' standing for flexibility

Narration: When the car exceeds electric range, it switches automatically to either petrol, or a biofuel or hydrogen.

John Lauckner: It's really to give us the flexibility of a range of propulsion systems and basically reduce and, over time, eliminate our dependency on petroleum fuels. It's really the electrification of vehicles on a scale that we haven't seen in the past

Narration: Whoa - did I just hear that ? Did the company that famously crushed all its electric cars only 3 years ago publicly announce the end of petrol and the age of electric?

If I had any doubts, this statement from the heartland of the combustion engine has clinched it.

No one knows what will ultimately win out. The car companies are hedging their bets -developing modular cars that will take any fuel plus electricity.

And if batteries continue to improve, the future will be fully electric.

In the meantime, I'm left wondering if I can hold off my new car purchase just another few years. Bring on the plug in hybrid.