AFP has the story:

Biodiesel has Hollywood backers like actress Julia Roberts and Morgan Freeman, is sung about by country star Willie Nelson but also meets the political correctness of the American right wing which has made the campaign against imported oil a mantra. “It’s better for the engine, way better for the environment, it’s cheaper, but it depends how you price your labor,” said Dan Goodman, an entrepreneur in residence at the University of Maryland Business School who runs his Mercedes on biodiesel.

Good point Dan. How much for some BioDiesel made by Julia Roberts?