The thieves had pulled a white van up to the back of the snazzy Chestnut Street restaurant Buddakan.

Were they stealing cash, or the giant golden Buddha? A stash of the popular "dip sum" doughnuts?

Nope. They were after the used cooking oil.

With biodiesel production increasing and prices for feedstocks - including used cooking oil - soaring, a waste product that restaurants once paid to get rid of is now a commodity targeted by thieves.

Greenworks Holdings, a group of companies that collect used cooking oil and convert it into biofuel, serves about 13,000 restaurants, mostly in the northeastern states.

"And we regularly lose used cooking oil from about 1,000 of those restaurants every month. It's ridiculous," said Ralph Tommaso, president of a subsidiary, the Association of Restaurant Owners for a Sustainable Earth, based in Lehigh Valley.

In the case of the purloined Buddakan oil, police responding to a 5 a.m. call on July 14 about suspicious activity in a lot off South Third Street found two men in a white van behind Buddakan. The vehicle, later impounded, was equipped with what Lt. Michael Young described as an "elaborate reservoir system": pipes and two tanks that he estimated at 300 gallons each.

Indeed, the setup was so intricate that officials, suspecting the worst, evacuated the area and closed streets.

An ordnance team quickly determined, however, that the stuff in the tanks wasn't explosive. Just slippery.

Arrested and charged with theft were Keith Williams, 23, of the 4500 block of Market Street, and Musayyeb Hunt, 42, of the 4700 block of North 11th Street.

Other places that have been hit include chicken restaurants in Camden and Willingboro, a pizzeria and a Mexican restaurant in Philadelphia, a diner in Clifton Heights, and a Chinese restaurant, pizzeria, and saloon in Glenolden, said Tommaso, also CEO of Greenworks Holdings.

Sometimes, the thieves come under cover of darkness and are gone before anyone knows they were there.

But at one Abington eatery, they posed as subcontractors for the oil-collection company.

At first, John Prisco, manager of the Steak & Hoagie Factory Store on York Road, didn't question the legitimacy of the men in the white van.

But he became suspicious when he came in early one morning and they skedaddled. "They pulled away too fast," he recalled. "They didn't say hi."

After police described a similar white van in the Buddakan oil heist, he realized his place might have been hit by the same guys.

Typically, restaurants put used cooking oil out back in bins provided by the collection companies.

In an effort to look legit, some thieves have even stolen stickers with the logos of oil collection companies. They peel them from restaurant oil bins and put them on their trucks.

In the past, the waste cooking oil was collected and used as a feed additive for livestock. But now, all the oil Greenworks collects - more than three million gallons a month - goes into fuel.

Tommaso said thefts seemed to spike in 2008, when the price of petroleum oil went to $150 a barrel and prices for other fuels rose correspondingly.

The price later dropped, but now it's rising again.

The U.S. Department of Energy's Alternative Fuels Data Center tracks quarterly prices. On March 30, it listed the per gallon price for B100 - pure biodiesel instead of a blend - at $4.31. That is the highest price since July 1, 2008, when it was $4.81

The high price reflects growing demand for biofuel.

Burning it produces fewer emissions than regular petroleum, and it's a way to help the country wean itself off foreign oil. Last year, the biodiesel industry had record production - more than one billion gallons, said Ben Evans, a spokesman for the National Biodiesel Board.

Pennsylvania is one of the major producers, with more than a dozen plants, he said.

Most biodiesel is made from soybean oil. But used cooking oil - referred to as yellow grease once it's been through an initial processing - is less expensive. So the industry would like to rely on it more, Evans said.

The yellow grease supply is limited, however, and not because Michelle Obama's healthy eating campaign is taking off. The stuff is still used as an animal feed additive and to produce soaps and detergents.

Tommaso's company pays restaurants up to $1 a gallon for used cooking oil, depending on quantity and quality. By his estimate, crooks could sell purloined oil for $2 a gallon. So if the Buddakan thieves had two 300-gallon tanks in the truck, they could fill them in a few hours and make $1,200.

With the rash of thefts, Tommaso said Greenworks was resorting to putting locking devices on oil-collection bins - a solution that will cost $6 million.

Domenico Finocchiaro, one of the owners of Eden Green Energy, a Philadelphia oil-collection company on Federal Street, said losing the oil isn't the only cost. To keep customers happy, Eden Green often pays them for oil that was stolen.

Frequently, the thieves are sloppy and spill oil, he said. So, again, to keep customers happy, Eden Green employees go clean it up.

And now, with thefts on the rise and oil-collection companies hurting, Finocchiaro worries that there may be a confrontation between thieves and legitimate drivers. Sooner or later, he said, it's going to happen.

Filing police reports is a waste of time, he said.

To police, "it looks like a victimless crime," said Tommaso, even though his business loses money paying for workers and trucks to collect oil that isn't there.

The thievery has become so rampant that legitimate companies are teaming up to make sure they don't buy oil from thieves. "Unfortunately, if we don't buy the oil, someone else will," Tommaso said.

In time, if security doesn't thwart thieves, the increasing green trend might.

Chris Moyer, sustainability manager for the National Restaurant Association, said some restaurants are installing equipment that will use their old cooking oil to produce energy for their own use.