And perhaps it is. It has become increasingly clear that it will not be possible to grow enough crops to cover global demand for food and fuel, especially as water is becoming scarce and pressure is mounting from the environmental lobby to conserve tropical rainforests and wildlife.

Over the past year, a biofuel boom worldwide has already sharply boosted agricultural prices, sparking worries over food supply as the world's population continues to grow.

David Jackson, an analyst at LMC International Ltd in London, calculated that the world would need an additional 100 million hectares of farmland if all countries were to blend 5 percent of biofuels into the cars --- as many envisage by 2015.

The required land, about half the size of Indonesia, would match roughly the total additional land available for farming on earth, including remote areas of Africa or Brazil.

"There's no perfect solution for ethanol or biodiesel from food crops, or from agriculture," Jackson told Reuters. "In total the amount of land available is roughly 100 million hectares worldwide ... But that's not all going to be developed."

The analysts said that while sugar was the most land-efficient feedstock for ethanol, it needed plenty of water.

It would take several years before the commercial use of the next generation technology, which would turn agricultural waste into fuel ethanol, they said.

For biodiesel, there is also no alternative feedstock to edible oils, such as palm oil or soyoil, in the foreseeable future, despite an enthusiasm for non-edible oils from oilseed plants like jatropha in countries such as India and China.

DREAM OR NIGHTMARE?

Another reason why the green dream is fading lies with the rocky economics of biofuel.

Oil prices have soared 40 percent this year but once-lowly palm oil has jumped by two-thirds. So now palm oil costs an astonishing US$735 a tonne, making crude a bargain at about US$593 a tonne.

Even in the United States, the world's top ethanol producer where the government provides generous subsidies, profits are squeezed at biofuel plants by high corn costs and low ethanol prices.

In Southeast Asia, home to the world's top producers of palm oil -- the most land-efficient vegetable oil -- many biodiesel projects have been also put on backburner due to the poor returns.

"While there has been a lot of optimism and bullishness for biofuels in 2006 ... a lot of announced plants have not transpired into actual construction," said Cherie Tan, vice president for corporate banking at Rabobank in Singapore.

"Many investors people have a wait-and-see approach now."

Tan estimated that less than a half of biofuels projects in the region had materialised, with total annual capacity in the region estimated around 250,000 tonnes.

INLFATION WOES

The rise in raw material prices for palm and corn is also setting off alarm bells for governments worried about the rising cost of basic foods.

Frank Gunstone, honorary professor at Scottish Crop Research Institute, said the world would need an additional 10 million tonnes of vegetable oils a year to meet demand from both the food and fuel sectors.

Global output of vegetable oils rose to 153 million in the last crop year from 100 million tonnes 10 years earlier. But the annual increase was 9 million tonnes at best, falling short of the required 10 million this decade.

"The shortfall will impinge on prices and is already doing so," Gunstone said.

To avoid the competition from the food sector, D1 Oils Plc a UK-based biodiesel maker, has picked jatropha, planting 175,000 hectares worldwide, including in India and Africa.

Graham Prince, a spokesman for D1 Oils, said though jatropha could be grown on barren, marginal land, it has yet to be developed into a commercial crop. Its leaves, nuts and seeds were toxic, yields random and it required hand-harvesting.

"We are right at the beginning of the history of jatropha as a commercial crop," he said.