FRANKFURT - Record fuel costs pushed hybrid cars to centre stage at the world's biggest car show this week but automakers argued over whether the rising popularity of petrol-electric vehicles was just the result of marketing hype.

Long sniffed at as a fad by European carmakers enamoured of modern diesel motors that can be just as fuel efficient, hybrids are on the ascendancy as even erstwhile sceptics fall into line and rush to offer products with an environmental halo.

"Woe to the company that ignores the customer," said Fritz Henderson, chairman of General Motors Europe, one of the seemingly few companies at the Frankfurt show not to trumpet a new hybrid offering or highlight its plans to make one.

Hybrids yoke a petrol or diesel engine to at least one electric motor and batteries that let cars run on electricity at low speeds and which recharge by capturing energy from braking.

They cost thousands more than standard engines, but are getting more of a look-in as petrol prices get painful and diesels remain rare in the crucial US market, where many customers think diesel motors belong in trucks, not cars.

Japan's Toyota Motor Corp, whose hybrid Prius model has been a runaway hit, thinks hybrids can gain more of a foothold in Europe's diesel heartland.

"We believe in 10 years' time the world will be filled with hybrid cars," Kazuo Okamoto, the world number-two carmaker's head of research and development, told reporters when asked if hybrids would ever be more than a niche product in Europe.

Costs are coming down and the technology is advancing, so hybrids won't be limited to just big cars and SUVs, he said, adding: "We are sure that in the future the technology will be used for smaller cars as well."

Toyota aims to sell around 20,000 Prius cars in Europe this year and around 1 million hybrids annually around the world by early in the next decade. Its premium Lexus brand forecasts that a quarter of its European sales next year will be hybrids.

Jeff Schuster, head of global forecasting at JD Power-LMC Automotive Forecasting, said the fact that premium carmaker BMW had joined DaimlerChrysler and GM to co-develop advanced hybrids, and that Mercedes-Benz showed two concept hybrids in Frankfurt, proved hybrids were no fad.

"They're hedging their bets in acknowledging that there is something to the hybrid technology in terms of consumers' wants and desires," he said.

But Europeans' embrace of diesels means hybrids won't ever have the same popularity here as in the United States, where Schuster said they could grab 3.5 per cent of the market by 2010-2012, the equivalent of 650,000 units a year.

That volume could actually double in the unlikely event that carmakers drive down the premiums they charge for hybrids, he added. A new Lexus RX 400h luxury hybrid SUV, for instance, costs some $12,000 more than its older and slightly less fancy equivalent with a conventional engine, he said.

"It's a smart purchase. People want to feel that they're doing the right thing," one senior US auto executive said of hybrid sales in the United States.

"That's fine for a small portion of the population, but what about customers who go into a showroom and say, 'Here's the monthly payment I can afford, show me what you got'."

Hybrids' triumphant rise underscores that fuel-cell cars remain far from commercially viable. Widespread sales of fuel-cell cars that run on hydrogen and emit only water are probably still at least a decade away, executives say.

All the attention on hybrids crowded out advances in other fuel-saving technology such as burning biomass or natural gas.

"Hybrid is perhaps an answer but there are other ones," said GM Europe President Carl-Peter Forster, noting that a natural gas vehicle cost half as much to run as a petrol-powered car and around a third less than a diesel.

"Let's not say hybrid is the solution to all our problems," he said, adding that politicians were wrong to give hybrids favoured treatment. Instead, they should set environmental standards and let the market decide how to meet them.