Used cooking oil has attracted growing attention in recent years as a cleaner, less expensive alternative to fossil fuels for vehicles. In many countries, including the United States, the oil is collected by companies and refined into a form of diesel. Some cities use it in specially modified municipal buses or vans. And the occasional environmentalist has experimented with individually filtering the oil and using it as fuel.
Here, however, the direct-to-the-tank approach is gaining a bit of mainstream popularity, attracting people like Mr. Roost, on his way to work, dressed in a suit. The oil, he said, is "good for the environment and it's cheaper than diesel, even now that prices have dropped." It costs $4.88 per gallon, which is about 10 percent less than diesel costs now -- and about one-third less than diesel cost at its peak last year. Used cooking oil will never erase the need for filling stations, nor will it, by itself, reverse climate change, transportation experts say.
"You can't eat enough French fries" to serve all the cars driven in the West, said Peder Jensen, a transport specialist at the European Environment Agency. At most, he said, cooking oil might supplant a few percent of diesel fuel consumption. But he said that it was one of many small adjustments that, added together, could have an important effect on reducing emissions of greenhouse gases.