In Europe it is mostly local rapeseed and sunflower oil, used to make diesel fuel. In a small number of instances, plant oil is used in place of diesel fuel, without further refinement.
But as many European countries push for more green energy, they are increasingly importing plant oils from the tropics, since there is simply not enough plant matter for fuel production at home.
On the surface, the environmental equation that supports biofuels is simple: Since they are derived from plants, biofuels absorb carbon while they are grown and release it when they are burned. In theory that neutralizes their emissions.
But the industry was promoted long before there was adequate research, said Reanne Creyghton, who runs Friends of the Earth's anti-palm oil campaign here.
Biofuelswatch, an environment group in Britain, now says that "biofuels should not automatically be classed as renewable energy." It supports a moratorium on subsidies until more research is done to determine whether various biofuels in different regions are produced in a manner that is ecologically responsible.
Beyond that, the group suggests that all emissions arising from the production of a biofuel be counted as emissions in the country where the fuel is actually used, providing a clearer accounting of environmental costs.
The demand for palm oil in Europe has skyrocketed in the last two decades, first for use in food and cosmetics, and more recently for fuel.
This versatile and cheap oil is used in about 10 percent of supermarket products, from chocolate to toothpaste, accounting for 21 percent of the global market for edible oils.
Palm oil produces the most energy of all vegetable oils for each unit of volume when burned. In much of Europe it is used as a substitute for diesel fuel, though in the Netherlands, the government has encouraged its use for electricity.
With hundreds of millions of euros in national subsidies, the Netherlands rapidly became the leading importer of palm oil in Europe, taking in 1.5 million tonnes last year, a figure that has been nearly doubling each year.
The increasing demand has created damage far away. Friends of the Earth estimates that 87 percent of the deforestation in Malaysia between 1985 and 2000 was caused by new palm oil plantations.
In Indonesia, the amount of land devoted to palm oil has increased 118 percent in the last eight years.
Then in December, scientists from Wetlands International released their calculations about the global emissions that palm farming on peatland caused.
Peat is an organic sponge that stores huge amounts of carbon, helping balance global emissions. Peatland is 90 percent water.
But when it is drained, the Wetlands International scientists say, the stored carbon gases are released into the atmosphere.
To makes matters worse, once dried, peatland is often burned to clear ground for plantations. The Dutch study estimated that the draining of peatland in Indonesia releases 660 million tonnes of carbon into the atmosphere a year and that fires contributed another 1.5 billion annually.
The total is equivalent to 8 percent of all global emissions caused annually by burning fossil fuels, the researchers said.
"These emissions generated by peat drainage in Indonesia were not counted before," Kaat said. "It was a totally ignored problem."