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JEREMY HOBSON: So a man walks into a bar -- What? think you've heard this one before? Well trust me, you've never heard this version. In Atlanta bar and restaurant owners are in the middle of a battle over their used cooking grease.

Reporter Jim Burress from WABE has the story.

Jim Burress: The second best thing about a bar? Bar food.

Standing in front of a bubbling deep fryer in the kitchen of Atlanta's Buckhead Bottle Bar, owner Ian Winslade says here, it's the Big Boy Burger and fries that are most popular.

Ian Winslade: We blanche the fries first at a lower temperature, then finish them back at a higher temperature.

Not on the menu, but lately just as popular is what's out the back door. Winslade peers into a mini-dumpster full of brown goo.

Winslade: I mean that's it. This is what the whole war's over.

Spent cooking oil. Used to be, restaurants had to pay companies to haul away their used cooking oil. In recent years, selling that yellow grease has become a half-billion dollar a year industry. So companies are now paying restaurants for the stuff. And that's pitting grease collector against grease collector.

Over the past few months, a company called Greenlight Biofuels has wooed away some 50 local restaurants from one of the biggest players in the grease business, Griffin Industries. And Griffin is fighting back with a lawsuit. The company's attorney is Katherine Hernacki.

Katherine Hernacki: Interference with contracts, conversion, trespass, and in the criminal arena, basic theft statues. Theft is theft.

But Greenlight's attorney, Jim Neale, says the litigation is just sour grapes over losing customers.

Jim Neale: It's very easy to make allegations in court. It's very difficult to prove those.

The whole Griffin/Greenlight clash doesn't surprise Tom Cook, who heads the National Renderers Association, a trade group for grease processors. He says you have to keep in mind, cooking oil is oil.

Tom Cook: Some people are discovering there is a value to this that they didn't realize was there before, and that's probably why there's as much competition for it.

And if you want in on the action, it's actually a traded commodity. Just ask for "Yellow Grease."

In Atlanta, I'm Jim Burress for Marketplace.