If it weren't for that pesky climate-change problem, petroleum would remain a great source of power. It's energy-dense, portable and (relatively) cheap. Remove the carbon and it would be perfect — which is essentially what researchers at Arizona State University (ASU) have been trying to do. Milton Sommerfeld and Qiang Hu have been working on raising algae to turn into a biofuel that would be virtually identical to gasoline. The fuel would actually be carbon-neutral, because algae consume carbon dioxide as they grow. Unlike traditional corn or sugarcane — two plants used for most ethanol biofuels today — algae can't be eaten, so using it for fuel doesn't cut into food supplies. ASU isn't alone. Start-ups like Sapphire Energy in San Diego are vying to bring the fuel to market — and give oil back its good name.