The potential to run engines on biofuel goes all the way back to Rudolph Diesel's successful trials using peanut oil a century ago.

Yet it is only now, with the transport sector likely to be the fastest growing contributor to greenhouse gas emissions this century, and diesel prices climbing steadily as oil appears scarcer and less secure, that the advantages of biodiesel are being appreciated by governments around the world. However, there is as yet no source of biodiesel that is cheap and plentiful enough to meet the potential demand. Running trucks on used cooking fat from fast food outlets is not going to be a large scale option.

However, across the developing world there's growing excitement about the possibility that an up-to-now obscure tree, Jatropha Curcus, might offer a sustainable, large scale source of biodiesel. This non-edible shrub is planted as a hedge in both Africa and India, and its beans are used as a laxative in traditional medicine. When crushed the beans produce oil that can be refined into biodiesel.

According to the International Energy Association, the use of oil, including diesel, for road transport will double in the next 25 years and greenhouses gases will increase commensurably. In the EU, legislation is already in place to mitigate this by increasing the proportion of biodiesel in Europe's transport energy mix. The EU biofuels directive requires a minimum level of biofuels as a proportion of fuels sold in the EU of 2% by 2005, 5.75% by 2010 and 20% by 2020. The main green fuels will be ethanol and biodiesel, and demand for biodiesel is expected to be up to 10.5 billion litres by 2010.

If that demand can be met, it will be good news for the environment and for our general health. While combustion of any fuel releases CO2 into the atmosphere, biodiesel produces lower emissions than mineral diesel. Furthermore, because it comes from crops that absorb CO2 as they grow, biodiesel's overall contribution to greenhouse gas emissions is extremely low. A 1998 biodiesel lifecycle study, jointly sponsored by the US Department of Energy (USDE) and the US Department of Agriculture, concluded that pure B100 biodiesel reduces net CO2 emissions by 100 percent compared to petroleum diesel. With a B20 mix (a 20% bio-diesel solution), the net CO2 emissions are reduced by 20%. Compared with mineral diesel, biodiesel reduces particle emissions (PM) by 30%, carbon monoxide (CO), which affects air quality and human health, by 50%, and sodium monoxide (SOx) by 50%. Unlike mineral diesel, bio-diesel is non-toxic and is biodegradable.