Julia Roberts is trying to make it easier for Daryl Hannah to fuel up.

Dallas-based biodiesel producer Earth Biofuels announced that Roberts will serve as a spokeswoman and chair the company's new advisory board, aiding the organization's quest to promote its environmentally friendly alternative fuel.

"It's very important that we expand our use of clean energy and make a long-term commitment to it," Roberts said in a statement, perhaps thinking of harmful effects pollution may have on her 20-month-old twins, Hazel Patricia and Phinnaeus Walter, in the future. "Biodiesel and ethanol are better for the environment and for the air we breathe."

The Oscar winner recently played a wood nymph, leafy crown and all, alongside George Clooney, Al Gore and Robert F. Kennedy Jr. on the cover of Vanity Fair's first-ever Green issue, which profiled various stars' efforts to promote environmental awareness.

Earth Biofuels said that Roberts will work with the company on a campaign to encourage the use of biodiesel in school buses nationwide.

Morgan Freeman and Willie Nelson also sit on the board of directors of Earth Biofuels and promote the use of renewable fuels.

In honor of Earth Day (or maybe it was just a coincidence), Roberts made her Broadway debut in April in Three Days of Rain. Despite mixed--well, mostly bad--reviews from critics, the Pretty Woman packed 'em in, playing to a sold-out house for 12 weeks.

Although she won't be joining Clooney and crew for Ocean's Thirteen this summer, Roberts is a member of a different type of tenacious gang in her upcoming film The Ant Bully, which comes out July 28. The Erin Brockovich star voices an ant named Hova in the animated film about a boy who terrorizes the ants in his yard but learns a thing or two when he's shrunken down to their size and forced to pull hard labor. Meryl Streep and Nicolas Cage also star.