NUNEATON, England — As he has done frequently over the last 18 months, Andy Roost drove his blue diesel Peugeot 205 onto a farm, where signs pointed one way for “eggs” and another for “oil.”
He unscrewed the gas cap and chatted nonchalantly as Colin Friedlos, the proprietor, poured three large jugs of used cooking oil — tinted green to indicate environmental benefit — into the Peugeot’s gas tank.
Mr. Friedlos operates one of hundreds of small plants in Britain that are processing, and often selling to private motorists, used cooking oil, which can be poured directly into unmodified diesel cars, from Fords to Mercedes.
Last year, when the price of crude oil topped $147 a barrel, a number of large companies in Europe and the United States were spurred to set up plants to collect and refine used cooking oil into biodiesel.
The global recession and the steep drop in oil prices have now killed many of those large refining ventures. But smaller, simpler ones like Mr. Friedlos’s are moving in to fill the void with their direct-to-tank product, having been deluged by offers of free oil from restaurants.
A tumble of tin containers now sit on the farm. Some dealers here offer fill-ups in suburban yards and barns. Others — like John Nicholson, founder of a small company in Wales — deliver jugs of green car fuel to the doors of hundreds of customers, much like a vehicular milkman.
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.
Dr. Jensen said that cooking oil fuel was “feasible” for diesel engines — Rudolf Diesel predicted that his engine, patented in the 1890s, would run on it — and that it was, “from an environmental point of view, a good idea, taking this waste and making it useful.”
The main barriers to the widespread use of cooking oil, Dr. Jensen said, are “structural,” like the lack of standards for processing the fuel and adapting and maintaining vehicles to run on it.
Others disagree. Stuart Johnson, manager of engineering and environment at Volkswagen of America, called putting raw vegetable oil in cars “a bad idea” and said, “We don’t recommend it.” The inconsistent quality of cooking oil fuel, he said, means that “it may contain impurities and it may be too viscous,” especially for newer, more complex diesel engines with injection systems.
None of that seems to stir concern in Mr. Nicholson, the Welsh entrepreneur. He said he first poured vegetable oil from his kitchen into the family car eight years ago, when the filling stations were emptied by a gas crisis. His wife, a nurse, had to get to work.
Over the next few years, he experimented with different techniques and started Bio-Power (UK), a national umbrella group to assist small producers like himself.
“People say, ‘I’ve got no choice but the regular filling station, and they sell only fossil fuel,’ ” Mr. Nicholson said. “You’ve got to think differently. This does challenge the status quo.”
Many diesel vehicles, particularly older models, run fine on cooking oil and do not need adaptation, he said. He said that he was lucky the car his wife was driving was “tolerant.”
But Dr. Jensen said it was safer to adapt cars for cooking oil use, an adjustment that can be done for about $300 and involves putting in a small heater to pre-warm fuel so that it is thinner, and installing injection nozzles that are somewhat wider. Thousands of kits have been sold in Europe and the United States, though it is illegal in America to sell cars that have been adapted.
But Dr. Jensen cautioned that drivers who used cooking oil fuel were taking a risk and might lose their warranty protection.
Vegetable oil is cleaner than either gas or diesel, producing virtually no carbon dioxide, the main greenhouse gas linked to climate change, and far fewer of the tiny airborne particles in pollution that are harmful to human health. But if the cooking oil is not adequately filtered or prepared for use in cars, studies show, it can also produce high levels of another chemical, NOx, the main component of smog.
A directive of the European Union stipulating that all fuel at the pump should contain 5.75 percent biofuel by 2010 encouraged many large corporations to jump into the market.
In Scotland, for instance, Argent Oils set up the largest plant in the world, capable of collecting 330 million pounds of used cooking oil a year to produce 45 million gallons of biodiesel.
Nor has the movement been limited to Europe. Towns in Texas and other states have engaged companies like Biodiesel Industries to collect local oil and convert it to biodiesel for municipal vehicles.
Officials in Westchester County, N.Y., recently announced that they would collect cooking oil from restaurants for a fleet of modified vehicles, including a Veggie Van that travels to schools to educate students about biofuel diesel.
Producers like Mr. Friedlos have taken advantage of simpler brews and lower overhead. Instead of being refined with explosive chemicals at large factories, the oil is simply filtered and mixed with an additive to thin it and make it burn better. And transport costs are minimal.
Used cooking oil is a problematic waste, which clogs sewers and pipes if tossed down the drain, forming huge, slimy stalactites in sewers, and killing wildlife if it gets into lakes and streams. In Britain, cooking oil cannot be sent to landfills. The oil was once used to make animal feed, but that is no longer allowed because of concerns about mad cow disease.
Two years ago, in the affluent London suburb of Leatherhead, Chris Leveritt starting filtering oil from his restaurant, Trattoria Vecchia, to run the family car. He is now creating a small commercial factory to produce 132 gallons a day in his backyard. Mr. Leveritt’s partner, a wine distributor, picks up jugs of used oil when he delivers wine to dozens of restaurants in and around London.
In Wales, Mr. Nicholson delivers cooking oil to the National Trust, the Royal Society for the Protection of Birds, and about 300 other customers, who like it because it contains no fossil fuel.
But still, many motorists hesitate, Mr. Leveritt said. “There is a lot of resistance,” he said, “to putting something into your precious car that you brewed in the kitchen sink.”