Terry Gross

The demand for oil increases each year, but the supply is not inexhaustible. Experts predict that within 30 years our oil energy sources will be depleted. In his book, The End of Oil: On the Edge of a Perilous New World, Roberts looks at the implications for the world in terms of the economy, politics and the environment, and what alternatives exist for oil. Roberts writes about the energy industry for Harper's magazine and for other national publications.

Underhill studies and tracks the habits of shoppers in order to learn the best way to lead them to make purchases. His retail consulting firm, Envirosell, has helped big-name companies such as McDonald's, Levi Strauss and Blockbuster to study their customers' browsing and buying habits. He's the author of the book Why We Buy, and the new book Call of the Mall.

Carley is the executive director of GRASP, The Global and Regional Asperger Syndrome Partnership. In 2000, he and his then 4-year-old son were diagnosed with Asperger's Syndrome. GRASP works to educate the public about the disorder.