"Ethanol today clearly has the biggest potential for clean buses," said Jonas Stroemberg of Stockholm Transport, SL, which runs public transportation throughout the county of Stockholm.

Speaking on the last day of the three-day "Clean Vehicles and Fuels" conference, which has focused on global warming and efforts to reduce greenhouse gases, Stroemberg raved about Sweden's experiences with ethanol-run buses.

"It's not difficult at all (to switch to ethanol). You just have to start doing it", he insisted.

Sweden today has the world's largest ethanol bus fleet. Last year, 253 buses ran on ethanol, an alcohol made of wheat, beetroot, corn or sugar cane, and next year the number is expected to jump to 400.

Switching to clean fuel is becoming a growing priority in Europe, where the European Union recently issued a directive urging governments to promote biofuels and other renewable energy sources for transportation as replacements for petrol and diesel.

The EU has set a 2005 consumption target of two percent, but Sweden, a front-runner in the field, has decided to take the bull by the horns and set a goal of three percent.

In the county of Stockholm, where about 70 percent of the two million inhabitants use the massive public transportation system, purifying the exhaust from buses is a major goal.

"We have tested almost every alternative energy and fuel source there is," Stroemberg said.

SL is using bio gas, a clean energy source made up of organic waste, in a number of its buses, but has found that the gas so far is not available in large quantities and that shifting to the new fuel source entails very expensive infrastructure costs.

Tests using hydrogen fuel cells, which offer no polluting emissions at all, also showed a lack of existing infrastructure and it proved difficult to find supplies of the spare parts needed.

Georg Feltz, a representative of the city of Luxemburg, also told the conference that city experiments with buses using batteries had come to naught after suppliers stopped producing vital parts needed to run the vehicles.

"The buses had to be taken out of service and garaged," he said.

Ethanol is on the other hand widely available, entails minimal extra costs and, most importantly, is a liquid fuel so infrastructure at fueling stations can remain largely unchanged, Stroemberg said.

"You have to secure your supply of fuels and these fuels should preferably be renewable ... We need to do this as cheaply as possible. We can't afford a lot of strange and experimental solutions," he told AFP after his talk.

By next year, Stockholm expects 25 percent of its buses to run on renewable fuels. By 2011, the number should be 50 percent, and by 2030 the county hopes that 100 percent of its buses will run on renewable fuels.

Fueling on ethanol could also help Sweden shake off its dependency on foreign oil.

"When it comes to production and imports of biofuels, we are ahead" in Europe, he said. Only Brazil and some states in the US are ahead of us," Martin Larsson, a Swedish environment ministry secretary, told AFP on the sidelines of the meeting.

The Scandinavian country produces 25 percent of its ethanol consumption at three plants, while the remaining 75 percent is imported mainly from Brazil.

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