An enterprising thief can steal four thousand dollars’ worth of grease in half an hour. Photograph by Christopher Griffith

A few months ago, in a clanging, hissing plant on the outskirts of Newark, a tanker truck backed up to a deep reservoir and delivered thousands of dollars’ worth of raw material—what people in the rendering industry sometimes refer to as “liquid gold.” The plant’s owner is a company called Dar Pro, and the C.E.O., Randall Stuewe, looked on while a hose from the truck gushed a brown fluid, filled with fine sediment and the occasional mysterious solid. Slowly, the pit became a pool, whose surface frothed and eddied and gave off a potent odor of old French fries, onion rings, and batter-fried shrimp. “Used cooking oil,” Stuewe told me. “We process two billion pounds a year.”

Stuewe, a former farm kid from Kansas with a wide girth and a booming voice, explained that for decades his company’s business model was simple: collect discarded animal parts from the food industry, render out the fat and proteins, and sell them to companies that make cosmetics, soap, fertilizer, and pet food. Fifty-nine billion pounds of animal parts are processed each year in the United States; Dar Pro, with a hundred and twenty plants in forty-two states, is the country’s largest processor. In 2010, the company, then known as Darling Rendering, bought its main competitor, Griffin Industries, and began operating under the name Darling International. Stuewe instituted the snappier “Dar Pro” as part of his efforts to improve rendering’s public image. “As an industry, I’d have to give us a C-minus, maybe a D,” he says. “We never told anybody what we were doing. And we did that because we were making money. Money is perceived as evil sometimes in this country—which is a whole other discussion.”

Dar Pro is now valued at two billion dollars, and its improved fortunes have come largely from used cooking oil, collected in steel bins behind restaurants all over the country. Not long ago, the oil was used mostly by livestock farmers, who spray it onto animal feed to fatten up hogs, chickens, and cows. Lately, it has found a new life, by being cleaned, filtered, and chemically modified into biofuel. The process isn’t tidy. The wastewater has to be cooked off, and the scraps of hash browns and wontons and buffalo wings filtered out—to say nothing of the old shoes, dirty diapers, and used hypodermic needles that can end up in a bin in a back alley. But used cooking oil, correctly processed, burns eighty per cent cleaner than fossil fuels, has a smaller carbon footprint than corn ethanol, and doesn’t compete with the food supply. Nathanael Greene, at the Natural Resources Defense Council, told me that it provides “probably the best of the biofuels out there.”

There isn’t enough grease to solve the energy crisis, but it does put a dent in the problem—and grease that’s converted isn’t dumped in landfills. To encourage biofuel production, governments have enacted incentives. According to a federal law passed in 2007, thirty-six billion gallons of biofuel must be blended into transportation fuel by 2022. There is also a dollar-a-gallon subsidy for refineries that mix renewable fuel into their products. This year, KLM Royal Dutch Airlines, in partnership with the Port Authority of New York and New Jersey, started a daily transatlantic flight powered by fuel that is twenty-five per cent converted fryer oil, collected at Cajun restaurants in Louisiana.

The increased demand has made the price of used cooking oil skyrocket. A decade ago, used grease traded on the Chicago commodities exchange for less than eight cents a pound. Now it can go for more than four times that price, providing criminals with a potent incentive to get at spent oil before renderers do. Thieves use bolt cutters to remove locks on container lids, or cut through steel with blowtorches; they use vacuum hoses to suck grease into tanker trucks. A thief driving down a strip-mall alleyway can collect four thousand dollars’ worth in half an hour. “It’s right up there next to Rolexes,” Stuewe told me. Dar Pro, he says, loses millions of dollars to theft each year.

Like other big renderers, Dar Pro has turned to security firms to protect its grease. In 2011, Stuewe hired Total Compliance Associates, a Manhattan-based firm headed by Stuart GraBois, a former U.S. assistant district attorney, and Mike Ferrandino, a former F.B.I. supervisor. When I visited the firm’s offices, in a Times Square high-rise, GraBois, an elegantly dressed, white-haired man, admitted that he was nonplussed when he got the call from Dar Pro. “I thought, Grease?” he said, laughing. “I didn’t want to say, ‘Who cares?’—but grease? Then you find out what a huge business it is, and how much they’re losing.”

In the past two years, GraBois and Ferrandino have pursued more than a hundred grease cases, using classic crime-busting techniques: surveillance and stakeouts, undercover operations, stings, hidden cameras. They still struggle to persuade law-enforcement officials to take grease theft seriously, but GraBois insisted that they’re making headway. “You speak to a prosecutor a year ago,” he said, “and it’s ‘What are you calling me about?’ Now I think it’s reached a point where they’re believing that it’s real.”

Not everyone is convinced that theft is the problem. Jon Jaworski is an attorney in Houston with a practice in family law and a sideline defending grease thieves. His first case, he said, was in 1986: “I had a couple of guys get busted in Galveston County at a Popeye’s Fried Chicken.” Back then, grease went for only a few pennies on the Chicago exchange, but, if you collected enough of it and knew where to sell it, you could make some money. Jaworski won the case, and then sued the renderer for malicious prosecution, winning a forty-two-thousand-dollar settlement. Accused thieves flooded his office. “I became the hero of all the little grease guys,” he says. His clients stank of rancid oil, and left greasy stains on his furniture, but Jaworski—a goateed man with slicked-back hair who collects Three Stooges memorabilia and exotic firearms—fell in love with the work. “They’re fun cases,” he says. “Lots of interesting characters.”

Since the advent of biodiesel, his typical defendant is as likely to be a guy with a science degree who runs a biofuel startup—“environmentalists,” Jaworski says. But the central issue in grease litigation remains the same, he told me: the national renderers like Dar Pro are not actually concerned with trying to stop grease theft, which he insists has a far smaller effect on their bottom line than they claim. “Half the time, they aren’t even paying restaurants for the grease,” he told me. Instead, Jaworski says, they are simply trying to crush independents and gain a monopoly.

His favorite case to illustrate that charge involves a fifty-four-year-old Houston native named Everett Henley. In the eighties and nineties, Henley ran a small rendering plant, buying spent cooking oil from the city’s haulers, cleaning it up, and selling it to feed companies. According to Griffin Industries, he was also the kingpin in a used-grease crime ring—and has still not entirely reformed. “Everett knows grease,” Jaworski says. “And they will do anything to get him out of business.”

Henley is a ruggedly built man, with a salt-and-pepper brush cut, a toothy smile, and a guileless good-ol’-boy manner. Many who work in grease grew up in the business; Henley came to it late. After high school, he did a couple of semesters of college, and worked for a time at his father’s engineering firm, but he hated being confined to a desk. He ran a car-repossession business, worked in a jewelry store. Then one day he put his name in for the fire department, and the city passed along his application to the police force. “I said, ‘What the heck. Why not?’ ” Henley told me. That’s how he became a cop. “I worked some pretty bad parts of town,” he says. “Then I went to Special Operations, where I did Presidential details, parades.” He liked the job, but it didn’t pay much, so he took on some hours as a security guard at the Galleria mall. There, he met a clothing-store manager named JoAnn Villegas, a brunette divorcée with two small kids. They started dating. JoAnn wanted to marry him right away, but when she saw his police paycheck—three hundred and sixty dollars a week—she was aghast. She told him that she had an idea for how to supplement his income.