CHICAGO (CBS) — Thieves call it “yellow gold.”

It is actually used cooking oil, stolen from dumpsters behind Chicago restaurants and sold. It’s a valuable commodity used to create bio fuels.

In fact, stealing the oil is a felony, but that isn’t stopping a growing black market, CBS 2’s Jim Williams reports.

Cesar Izquierdo of Taste of Peru on North Clark Street in Rogers Park, has been hit by the thieves.

They don’t care about what’s inside the establishment.

It’s something out back–the used grease–in dumpsters out back in the alley.

“People are taking our grease, back here out in the alley,” he said.

Three times, recently, he says.

The oil is then sold by the crooks to refiners, which turn it into bio fuel.

The black market has been called the Wild, Wild West of the grease industry. And it is harming legitimate businesses, like Ace Grease, who legitimately collect the oil and sell it.

It is hard to regulate, because, a representative with Ace Grease said, used cooking oil doesn’t have a serial number.

It also leaves a massive mess at his business, Izquierdo said.

“You see grease all over the place,” he said. “Cars going by spray it all around.”