HEBER CITY, Utah (AP) — Bill Hartlieb's welding shop smells like restaurant grease.

That's because Hartlieb has set up a small-scale refinery to recycle used vegetable oils from dining establishments into biodiesel fuel to power cars and trucks.

He's among a growing number of Utahns — fed up with high gas prices — who are using and making biodiesel and straight vegetable oil fuel, or SVO. The practice is illegal under federal law.

Hartlieb, however, disputes the hobby violates the Clean Air Act. He says vegetable oil fuels release fewer emissions than petroleum.

"I think it's really kind of a gray issue," he said.

Hartlieb makes about 20 percent of the fuel he needs. He buys the rest at a Park City station that sells biodiesel.

The growing popularity of home-based vegetable oil-based fuel production may be fraught with legal consequences. The federal Environmental Protection Agency has a list of companies certified to convert vehicles to alternative fuel. No companies for SVO kits are listed, although one is testing with the EPA.

"Basically, all diesel fuels and gasoline fuels and fuel additives are required to be registered with the EPA," says Jeff Kimes, a Denver-based EPA environmental engineer.

Penalties for mechanics and companies that convert vehicles to run on vegetable max out at $32,500 per violation, per day. Some investigations are under way.

It's also against Utah tax laws to burn biodiesel without paying fuel taxes, Utah State Tax Commission spokesman Charlie Roberts. Driver pay at the pump, and home-based biodiesel fuel makers should be paying too, Roberts said.

"A biodiesel fuel is a special fuel, and so they should be filling out a special user return and paying the 24.5 cents tax per gallon," Roberts says.

The Tax Commission, however, wouldn't tax SVO fuel because is illegal and not sold by retailers in the United States.

Biodiesel sold by retailers is legal, but the same material produced at a private garage is not, unless its certified by ASTM International, an organization of technical, consumer and government experts.

In Utah, about 20 stations sell biodiesel from Logan to Moab.

Syracuse resident Graydon Blair sells supplies for making biodiesel over the Internet. He started the business on the side in 2005. He now ships more than 100 orders weekly and quit his day job at Intermountain Healthcare. Only about 1 percent of his business is in Utah.

Blair says most biodiesel- and SVO-makers in Utah have gone "underground" after a spat between fuel-makers and grease-collection and rendering companies. The issue ended up before the Salt Lake Valley Health Department, which regulates transporting and disposing of wastes.

It's now illegal to collect grease from Salt Lake County restaurants without a permit.

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Information from: Deseret News, http://www.deseretnews.com