Country star Willie Nelson has his wife to thank for getting him involved in biodiesel fuel after she quizzed him about cars that run on vegetable oil.

The singer/songwriter has become an unlikely alternative energy executive after founding the BioWillie fuel company, which boasts its own truck stop in Texas, and it all started with a Volkswagen Jetta that ran on used cooking fat.

He explains, "Three years ago my wife came to me and said, 'What do you think about buying a biodiesel car? It runs on vegetable oil from all the restaurants around here, and you recycle it, then you put it in your diesel engine.'"

And when Nelson realised his wife's car was working perfectly with the recycled oil fuel, he thought he'd try it out on a Mercedes Benz.

He adds, "I bought a diesel Mercedes and had it filled up with 100 per cent vegetable oil. I heard rumours that the Mercedes people were nervous because they didn't know if it would ruin the engine. But it ran like a sewing machine.

"I've never put anything in it besides 100 per cent pure vegetable oil. It runs cleaner, and with better mileage."